From 6eb9c5a5657d1fe77b55cc261450f3538d35a94d Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 4 May 2024 14:19:15 +0200 Subject: Adding upstream version 13.4. Signed-off-by: Daniel Baumann --- doc/src/sgml/ecpg.sgml | 9814 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 9814 insertions(+) create mode 100644 doc/src/sgml/ecpg.sgml (limited to 'doc/src/sgml/ecpg.sgml') diff --git a/doc/src/sgml/ecpg.sgml b/doc/src/sgml/ecpg.sgml new file mode 100644 index 0000000..84df3c3 --- /dev/null +++ b/doc/src/sgml/ecpg.sgml @@ -0,0 +1,9814 @@ + + + + <application>ECPG</application> — Embedded <acronym>SQL</acronym> in C + + embedded SQLin C + C + ECPG + + + This chapter describes the embedded SQL package + for PostgreSQL. It was written by + Linus Tolke (linus@epact.se) and Michael Meskes + (meskes@postgresql.org). Originally it was written to work with + C. It also works with C++, but + it does not recognize all C++ constructs yet. + + + + This documentation is quite incomplete. But since this + interface is standardized, additional information can be found in + many resources about SQL. + + + + The Concept + + + An embedded SQL program consists of code written in an ordinary + programming language, in this case C, mixed with SQL commands in + specially marked sections. To build the program, the source code (*.pgc) + is first passed through the embedded SQL preprocessor, which converts it + to an ordinary C program (*.c), and afterwards it can be processed by a C + compiler. (For details about the compiling and linking see ). + Converted ECPG applications call functions in the libpq library + through the embedded SQL library (ecpglib), and communicate with + the PostgreSQL server using the normal frontend-backend protocol. + + + + Embedded SQL has advantages over other methods + for handling SQL commands from C code. First, it + takes care of the tedious passing of information to and from + variables in your C program. Second, the SQL + code in the program is checked at build time for syntactical + correctness. Third, embedded SQL in C is + specified in the SQL standard and supported by + many other SQL database systems. The + PostgreSQL implementation is designed to match this + standard as much as possible, and it is usually possible to port + embedded SQL programs written for other SQL + databases to PostgreSQL with relative + ease. + + + + As already stated, programs written for the embedded + SQL interface are normal C programs with special + code inserted to perform database-related actions. This special + code always has the form: + +EXEC SQL ...; + + These statements syntactically take the place of a C statement. + Depending on the particular statement, they can appear at the + global level or within a function. Embedded + SQL statements follow the case-sensitivity rules of + normal SQL code, and not those of C. Also they allow nested + C-style comments that are part of the SQL standard. The C part of the + program, however, follows the C standard of not accepting nested comments. + + + + The following sections explain all the embedded SQL statements. + + + + + Managing Database Connections + + + This section describes how to open, close, and switch database + connections. + + + + Connecting to the Database Server + + + One connects to a database using the following statement: + +EXEC SQL CONNECT TO target AS connection-name USER user-name; + + The target can be specified in the + following ways: + + + + + dbname@hostname:port + + + + + + tcp:postgresql://hostname:port/dbname?options + + + + + + unix:postgresql://hostname:port/dbname?options + + + + + + an SQL string literal containing one of the above forms + + + + + + a reference to a character variable containing one of the above forms (see examples) + + + + + + DEFAULT + + + + + If you specify the connection target literally (that is, not + through a variable reference) and you don't quote the value, then + the case-insensitivity rules of normal SQL are applied. In that + case you can also double-quote the individual parameters separately + as needed. In practice, it is probably less error-prone to use a + (single-quoted) string literal or a variable reference. The + connection target DEFAULT initiates a connection + to the default database under the default user name. No separate + user name or connection name can be specified in that case. + + + + There are also different ways to specify the user name: + + + + + username + + + + + + username/password + + + + + + username IDENTIFIED BY password + + + + + + username USING password + + + + + As above, the parameters username and + password can be an SQL identifier, an + SQL string literal, or a reference to a character variable. + + + + If the connection target includes any options, + those consist of + keyword=value + specifications separated by ampersands (&). + The allowed key words are the same ones recognized + by libpq (see + ). Spaces are ignored before + any keyword or value, + though not within or after one. Note that there is no way to + write & within a value. + + + + The connection-name is used to handle + multiple connections in one program. It can be omitted if a + program uses only one connection. The most recently opened + connection becomes the current connection, which is used by default + when an SQL statement is to be executed (see later in this + chapter). + + + + If untrusted users have access to a database that has not adopted a + secure schema usage pattern, + begin each session by removing publicly-writable schemas + from search_path. For example, + add options=-c search_path= + to options, or + issue EXEC SQL SELECT pg_catalog.set_config('search_path', '', + false); after connecting. This consideration is not specific to + ECPG; it applies to every interface for executing arbitrary SQL commands. + + + + Here are some examples of CONNECT statements: + +EXEC SQL CONNECT TO mydb@sql.mydomain.com; + +EXEC SQL CONNECT TO unix:postgresql://sql.mydomain.com/mydb AS myconnection USER john; + +EXEC SQL BEGIN DECLARE SECTION; +const char *target = "mydb@sql.mydomain.com"; +const char *user = "john"; +const char *passwd = "secret"; +EXEC SQL END DECLARE SECTION; + ... +EXEC SQL CONNECT TO :target USER :user USING :passwd; +/* or EXEC SQL CONNECT TO :target USER :user/:passwd; */ + + The last form makes use of the variant referred to above as + character variable reference. You will see in later sections how C + variables can be used in SQL statements when you prefix them with a + colon. + + + + Be advised that the format of the connection target is not + specified in the SQL standard. So if you want to develop portable + applications, you might want to use something based on the last + example above to encapsulate the connection target string + somewhere. + + + + + Choosing a Connection + + + SQL statements in embedded SQL programs are by default executed on + the current connection, that is, the most recently opened one. If + an application needs to manage multiple connections, then there are + two ways to handle this. + + + + The first option is to explicitly choose a connection for each SQL + statement, for example: + +EXEC SQL AT connection-name SELECT ...; + + This option is particularly suitable if the application needs to + use several connections in mixed order. + + + + If your application uses multiple threads of execution, they cannot share a + connection concurrently. You must either explicitly control access to the connection + (using mutexes) or use a connection for each thread. + + + + The second option is to execute a statement to switch the current + connection. That statement is: + +EXEC SQL SET CONNECTION connection-name; + + This option is particularly convenient if many statements are to be + executed on the same connection. + + + + Here is an example program managing multiple database connections: + + +EXEC SQL BEGIN DECLARE SECTION; + char dbname[1024]; +EXEC SQL END DECLARE SECTION; + +int +main() +{ + EXEC SQL CONNECT TO testdb1 AS con1 USER testuser; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + EXEC SQL CONNECT TO testdb2 AS con2 USER testuser; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + EXEC SQL CONNECT TO testdb3 AS con3 USER testuser; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + /* This query would be executed in the last opened database "testdb3". */ + EXEC SQL SELECT current_database() INTO :dbname; + printf("current=%s (should be testdb3)\n", dbname); + + /* Using "AT" to run a query in "testdb2" */ + EXEC SQL AT con2 SELECT current_database() INTO :dbname; + printf("current=%s (should be testdb2)\n", dbname); + + /* Switch the current connection to "testdb1". */ + EXEC SQL SET CONNECTION con1; + + EXEC SQL SELECT current_database() INTO :dbname; + printf("current=%s (should be testdb1)\n", dbname); + + EXEC SQL DISCONNECT ALL; + return 0; +} +]]> + + This example would produce this output: + +current=testdb3 (should be testdb3) +current=testdb2 (should be testdb2) +current=testdb1 (should be testdb1) + + + + + + Closing a Connection + + + To close a connection, use the following statement: + +EXEC SQL DISCONNECT connection; + + The connection can be specified + in the following ways: + + + + + connection-name + + + + + + DEFAULT + + + + + + CURRENT + + + + + + ALL + + + + + If no connection name is specified, the current connection is + closed. + + + + It is good style that an application always explicitly disconnect + from every connection it opened. + + + + + + + Running SQL Commands + + + Any SQL command can be run from within an embedded SQL application. + Below are some examples of how to do that. + + + + Executing SQL Statements + + + Creating a table: + +EXEC SQL CREATE TABLE foo (number integer, ascii char(16)); +EXEC SQL CREATE UNIQUE INDEX num1 ON foo(number); +EXEC SQL COMMIT; + + + + + Inserting rows: + +EXEC SQL INSERT INTO foo (number, ascii) VALUES (9999, 'doodad'); +EXEC SQL COMMIT; + + + + + Deleting rows: + +EXEC SQL DELETE FROM foo WHERE number = 9999; +EXEC SQL COMMIT; + + + + + Updates: + +EXEC SQL UPDATE foo + SET ascii = 'foobar' + WHERE number = 9999; +EXEC SQL COMMIT; + + + + + SELECT statements that return a single result + row can also be executed using + EXEC SQL directly. To handle result sets with + multiple rows, an application has to use a cursor; + see below. (As a special case, an + application can fetch multiple rows at once into an array host + variable; see .) + + + + Single-row select: + +EXEC SQL SELECT foo INTO :FooBar FROM table1 WHERE ascii = 'doodad'; + + + + + Also, a configuration parameter can be retrieved with the + SHOW command: + +EXEC SQL SHOW search_path INTO :var; + + + + + The tokens of the form + :something are + host variables, that is, they refer to + variables in the C program. They are explained in . + + + + + Using Cursors + + + To retrieve a result set holding multiple rows, an application has + to declare a cursor and fetch each row from the cursor. The steps + to use a cursor are the following: declare a cursor, open it, fetch + a row from the cursor, repeat, and finally close it. + + + + Select using cursors: + +EXEC SQL DECLARE foo_bar CURSOR FOR + SELECT number, ascii FROM foo + ORDER BY ascii; +EXEC SQL OPEN foo_bar; +EXEC SQL FETCH foo_bar INTO :FooBar, DooDad; +... +EXEC SQL CLOSE foo_bar; +EXEC SQL COMMIT; + + + + + For more details about declaration of the cursor, + see , and + see for FETCH command + details. + + + + + The ECPG DECLARE command does not actually + cause a statement to be sent to the PostgreSQL backend. The + cursor is opened in the backend (using the + backend's DECLARE command) at the point when + the OPEN command is executed. + + + + + + Managing Transactions + + + In the default mode, statements are committed only when + EXEC SQL COMMIT is issued. The embedded SQL + interface also supports autocommit of transactions (similar to + psql's default behavior) via the + command-line option to ecpg (see ) or via the EXEC SQL SET AUTOCOMMIT TO + ON statement. In autocommit mode, each command is + automatically committed unless it is inside an explicit transaction + block. This mode can be explicitly turned off using EXEC + SQL SET AUTOCOMMIT TO OFF. + + + + The following transaction management commands are available: + + + + EXEC SQL COMMIT + + + Commit an in-progress transaction. + + + + + + EXEC SQL ROLLBACK + + + Roll back an in-progress transaction. + + + + + + EXEC SQL PREPARE TRANSACTION transaction_id + + + Prepare the current transaction for two-phase commit. + + + + + + EXEC SQL COMMIT PREPARED transaction_id + + + Commit a transaction that is in prepared state. + + + + + + EXEC SQL ROLLBACK PREPARED transaction_id + + + Roll back a transaction that is in prepared state. + + + + + + EXEC SQL SET AUTOCOMMIT TO ON + + + Enable autocommit mode. + + + + + + EXEC SQL SET AUTOCOMMIT TO OFF + + + Disable autocommit mode. This is the default. + + + + + + + + + Prepared Statements + + + When the values to be passed to an SQL statement are not known at + compile time, or the same statement is going to be used many + times, then prepared statements can be useful. + + + + The statement is prepared using the + command PREPARE. For the values that are not + known yet, use the + placeholder ?: + +EXEC SQL PREPARE stmt1 FROM "SELECT oid, datname FROM pg_database WHERE oid = ?"; + + + + + If a statement returns a single row, the application can + call EXECUTE after + PREPARE to execute the statement, supplying the + actual values for the placeholders with a USING + clause: + +EXEC SQL EXECUTE stmt1 INTO :dboid, :dbname USING 1; + + + + + If a statement returns multiple rows, the application can use a + cursor declared based on the prepared statement. To bind input + parameters, the cursor must be opened with + a USING clause: + +EXEC SQL PREPARE stmt1 FROM "SELECT oid,datname FROM pg_database WHERE oid > ?"; +EXEC SQL DECLARE foo_bar CURSOR FOR stmt1; + +/* when end of result set reached, break out of while loop */ +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +EXEC SQL OPEN foo_bar USING 100; +... +while (1) +{ + EXEC SQL FETCH NEXT FROM foo_bar INTO :dboid, :dbname; + ... +} +EXEC SQL CLOSE foo_bar; + + + + + When you don't need the prepared statement anymore, you should + deallocate it: + +EXEC SQL DEALLOCATE PREPARE name; + + + + + For more details about PREPARE, + see . Also + see for more details about using + placeholders and input parameters. + + + + + + Using Host Variables + + + In you saw how you can execute SQL + statements from an embedded SQL program. Some of those statements + only used fixed values and did not provide a way to insert + user-supplied values into statements or have the program process + the values returned by the query. Those kinds of statements are + not really useful in real applications. This section explains in + detail how you can pass data between your C program and the + embedded SQL statements using a simple mechanism called + host variables. In an embedded SQL program we + consider the SQL statements to be guests in the C + program code which is the host language. Therefore + the variables of the C program are called host + variables. + + + + Another way to exchange values between PostgreSQL backends and ECPG + applications is the use of SQL descriptors, described + in . + + + + Overview + + + Passing data between the C program and the SQL statements is + particularly simple in embedded SQL. Instead of having the + program paste the data into the statement, which entails various + complications, such as properly quoting the value, you can simply + write the name of a C variable into the SQL statement, prefixed by + a colon. For example: + +EXEC SQL INSERT INTO sometable VALUES (:v1, 'foo', :v2); + + This statement refers to two C variables named + v1 and v2 and also uses a + regular SQL string literal, to illustrate that you are not + restricted to use one kind of data or the other. + + + + This style of inserting C variables in SQL statements works + anywhere a value expression is expected in an SQL statement. + + + + + Declare Sections + + + To pass data from the program to the database, for example as + parameters in a query, or to pass data from the database back to + the program, the C variables that are intended to contain this + data need to be declared in specially marked sections, so the + embedded SQL preprocessor is made aware of them. + + + + This section starts with: + +EXEC SQL BEGIN DECLARE SECTION; + + and ends with: + +EXEC SQL END DECLARE SECTION; + + Between those lines, there must be normal C variable declarations, + such as: + +int x = 4; +char foo[16], bar[16]; + + As you can see, you can optionally assign an initial value to the variable. + The variable's scope is determined by the location of its declaring + section within the program. + You can also declare variables with the following syntax which implicitly + creates a declare section: + +EXEC SQL int i = 4; + + You can have as many declare sections in a program as you like. + + + + The declarations are also echoed to the output file as normal C + variables, so there's no need to declare them again. Variables + that are not intended to be used in SQL commands can be declared + normally outside these special sections. + + + + The definition of a structure or union also must be listed inside + a DECLARE section. Otherwise the preprocessor cannot + handle these types since it does not know the definition. + + + + + Retrieving Query Results + + + Now you should be able to pass data generated by your program into + an SQL command. But how do you retrieve the results of a query? + For that purpose, embedded SQL provides special variants of the + usual commands SELECT and + FETCH. These commands have a special + INTO clause that specifies which host variables + the retrieved values are to be stored in. + SELECT is used for a query that returns only + single row, and FETCH is used for a query that + returns multiple rows, using a cursor. + + + + Here is an example: + +/* + * assume this table: + * CREATE TABLE test1 (a int, b varchar(50)); + */ + +EXEC SQL BEGIN DECLARE SECTION; +int v1; +VARCHAR v2; +EXEC SQL END DECLARE SECTION; + + ... + +EXEC SQL SELECT a, b INTO :v1, :v2 FROM test; + + So the INTO clause appears between the select + list and the FROM clause. The number of + elements in the select list and the list after + INTO (also called the target list) must be + equal. + + + + Here is an example using the command FETCH: + +EXEC SQL BEGIN DECLARE SECTION; +int v1; +VARCHAR v2; +EXEC SQL END DECLARE SECTION; + + ... + +EXEC SQL DECLARE foo CURSOR FOR SELECT a, b FROM test; + + ... + +do +{ + ... + EXEC SQL FETCH NEXT FROM foo INTO :v1, :v2; + ... +} while (...); + + Here the INTO clause appears after all the + normal clauses. + + + + + + Type Mapping + + + When ECPG applications exchange values between the PostgreSQL + server and the C application, such as when retrieving query + results from the server or executing SQL statements with input + parameters, the values need to be converted between PostgreSQL + data types and host language variable types (C language data + types, concretely). One of the main points of ECPG is that it + takes care of this automatically in most cases. + + + + In this respect, there are two kinds of data types: Some simple + PostgreSQL data types, such as integer + and text, can be read and written by the application + directly. Other PostgreSQL data types, such + as timestamp and numeric can only be + accessed through special library functions; see + . + + + + shows which PostgreSQL + data types correspond to which C data types. When you wish to + send or receive a value of a given PostgreSQL data type, you + should declare a C variable of the corresponding C data type in + the declare section. + + + + Mapping Between PostgreSQL Data Types and C Variable Types + + + + PostgreSQL data type + Host variable type + + + + + + smallint + short + + + + integer + int + + + + bigint + long long int + + + + decimal + decimalThis type can only be accessed through special library functions; see . + + + + numeric + numeric + + + + real + float + + + + double precision + double + + + + smallserial + short + + + + serial + int + + + + bigserial + long long int + + + + oid + unsigned int + + + + character(n), varchar(n), text + char[n+1], VARCHAR[n+1] + + + + name + char[NAMEDATALEN] + + + + timestamp + timestamp + + + + interval + interval + + + + date + date + + + + boolean + booldeclared in ecpglib.h if not native + + + + bytea + char *, bytea[n] + + + +
+ + + Handling Character Strings + + + To handle SQL character string data types, such + as varchar and text, there are two + possible ways to declare the host variables. + + + + One way is using char[], an array + of char, which is the most common way to handle + character data in C. + +EXEC SQL BEGIN DECLARE SECTION; + char str[50]; +EXEC SQL END DECLARE SECTION; + + Note that you have to take care of the length yourself. If you + use this host variable as the target variable of a query which + returns a string with more than 49 characters, a buffer overflow + occurs. + + + + The other way is using the VARCHAR type, which is a + special type provided by ECPG. The definition on an array of + type VARCHAR is converted into a + named struct for every variable. A declaration like: + +VARCHAR var[180]; + + is converted into: + +struct varchar_var { int len; char arr[180]; } var; + + The member arr hosts the string + including a terminating zero byte. Thus, to store a string in + a VARCHAR host variable, the host variable has to be + declared with the length including the zero byte terminator. The + member len holds the length of the + string stored in the arr without the + terminating zero byte. When a host variable is used as input for + a query, if strlen(arr) + and len are different, the shorter one + is used. + + + + VARCHAR can be written in upper or lower case, but + not in mixed case. + + + + char and VARCHAR host variables can + also hold values of other SQL types, which will be stored in + their string forms. + + + + + Accessing Special Data Types + + + ECPG contains some special types that help you to interact easily + with some special data types from the PostgreSQL server. In + particular, it has implemented support for the + numeric, decimal, date, timestamp, + and interval types. These data types cannot usefully be + mapped to primitive host variable types (such + as int, long long int, + or char[]), because they have a complex internal + structure. Applications deal with these types by declaring host + variables in special types and accessing them using functions in + the pgtypes library. The pgtypes library, described in detail + in contains basic functions to deal + with those types, such that you do not need to send a query to + the SQL server just for adding an interval to a time stamp for + example. + + + + The follow subsections describe these special data types. For + more details about pgtypes library functions, + see . + + + + timestamp, date + + + Here is a pattern for handling timestamp variables + in the ECPG host application. + + + + First, the program has to include the header file for the + timestamp type: + +#include <pgtypes_timestamp.h> + + + + + Next, declare a host variable as type timestamp in + the declare section: + +EXEC SQL BEGIN DECLARE SECTION; +timestamp ts; +EXEC SQL END DECLARE SECTION; + + + + + And after reading a value into the host variable, process it + using pgtypes library functions. In following example, the + timestamp value is converted into text (ASCII) form + with the PGTYPEStimestamp_to_asc() + function: + +EXEC SQL SELECT now()::timestamp INTO :ts; + +printf("ts = %s\n", PGTYPEStimestamp_to_asc(ts)); + + This example will show some result like following: + +ts = 2010-06-27 18:03:56.949343 + + + + + In addition, the DATE type can be handled in the same way. The + program has to include pgtypes_date.h, declare a host variable + as the date type and convert a DATE value into a text form using + PGTYPESdate_to_asc() function. For more details about the + pgtypes library functions, see . + + + + + interval + + + The handling of the interval type is also similar + to the timestamp and date types. It + is required, however, to allocate memory for + an interval type value explicitly. In other words, + the memory space for the variable has to be allocated in the + heap memory, not in the stack memory. + + + + Here is an example program: + +#include <stdio.h> +#include <stdlib.h> +#include <pgtypes_interval.h> + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + interval *in; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + in = PGTYPESinterval_new(); + EXEC SQL SELECT '1 min'::interval INTO :in; + printf("interval = %s\n", PGTYPESinterval_to_asc(in)); + PGTYPESinterval_free(in); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} + + + + + + numeric, decimal + + + The handling of the numeric + and decimal types is similar to the + interval type: It requires defining a pointer, + allocating some memory space on the heap, and accessing the + variable using the pgtypes library functions. For more details + about the pgtypes library functions, + see . + + + + No functions are provided specifically for + the decimal type. An application has to convert it + to a numeric variable using a pgtypes library + function to do further processing. + + + + Here is an example program handling numeric + and decimal type variables. + +#include <stdio.h> +#include <stdlib.h> +#include <pgtypes_numeric.h> + +EXEC SQL WHENEVER SQLERROR STOP; + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + numeric *num; + numeric *num2; + decimal *dec; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + num = PGTYPESnumeric_new(); + dec = PGTYPESdecimal_new(); + + EXEC SQL SELECT 12.345::numeric(4,2), 23.456::decimal(4,2) INTO :num, :dec; + + printf("numeric = %s\n", PGTYPESnumeric_to_asc(num, 0)); + printf("numeric = %s\n", PGTYPESnumeric_to_asc(num, 1)); + printf("numeric = %s\n", PGTYPESnumeric_to_asc(num, 2)); + + /* Convert decimal to numeric to show a decimal value. */ + num2 = PGTYPESnumeric_new(); + PGTYPESnumeric_from_decimal(dec, num2); + + printf("decimal = %s\n", PGTYPESnumeric_to_asc(num2, 0)); + printf("decimal = %s\n", PGTYPESnumeric_to_asc(num2, 1)); + printf("decimal = %s\n", PGTYPESnumeric_to_asc(num2, 2)); + + PGTYPESnumeric_free(num2); + PGTYPESdecimal_free(dec); + PGTYPESnumeric_free(num); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} + + + + + + bytea + + + The handling of the bytea type is similar to + that of VARCHAR. The definition on an array of type + bytea is converted into a named struct for every + variable. A declaration like: + +bytea var[180]; + + is converted into: + +struct bytea_var { int len; char arr[180]; } var; + + The member arr hosts binary format + data. It can also handle '\0' as part of + data, unlike VARCHAR. + The data is converted from/to hex format and sent/received by + ecpglib. + + + + + bytea variable can be used only when + is set to hex. + + + + + + + Host Variables with Nonprimitive Types + + + As a host variable you can also use arrays, typedefs, structs, and + pointers. + + + + Arrays + + + There are two use cases for arrays as host variables. The first + is a way to store some text string in char[] + or VARCHAR[], as + explained in . The second use case is to + retrieve multiple rows from a query result without using a + cursor. Without an array, to process a query result consisting + of multiple rows, it is required to use a cursor and + the FETCH command. But with array host + variables, multiple rows can be received at once. The length of + the array has to be defined to be able to accommodate all rows, + otherwise a buffer overflow will likely occur. + + + + Following example scans the pg_database + system table and shows all OIDs and names of the available + databases: + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + int dbid[8]; + char dbname[8][16]; + int i; +EXEC SQL END DECLARE SECTION; + + memset(dbname, 0, sizeof(char)* 16 * 8); + memset(dbid, 0, sizeof(int) * 8); + + EXEC SQL CONNECT TO testdb; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + /* Retrieve multiple rows into arrays at once. */ + EXEC SQL SELECT oid,datname INTO :dbid, :dbname FROM pg_database; + + for (i = 0; i < 8; i++) + printf("oid=%d, dbname=%s\n", dbid[i], dbname[i]); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} + + + This example shows following result. (The exact values depend on + local circumstances.) + +oid=1, dbname=template1 +oid=11510, dbname=template0 +oid=11511, dbname=postgres +oid=313780, dbname=testdb +oid=0, dbname= +oid=0, dbname= +oid=0, dbname= + + + + + + Structures + + + A structure whose member names match the column names of a query + result, can be used to retrieve multiple columns at once. The + structure enables handling multiple column values in a single + host variable. + + + + The following example retrieves OIDs, names, and sizes of the + available databases from the pg_database + system table and using + the pg_database_size() function. In this + example, a structure variable dbinfo_t with + members whose names match each column in + the SELECT result is used to retrieve one + result row without putting multiple host variables in + the FETCH statement. + +EXEC SQL BEGIN DECLARE SECTION; + typedef struct + { + int oid; + char datname[65]; + long long int size; + } dbinfo_t; + + dbinfo_t dbval; +EXEC SQL END DECLARE SECTION; + + memset(&dbval, 0, sizeof(dbinfo_t)); + + EXEC SQL DECLARE cur1 CURSOR FOR SELECT oid, datname, pg_database_size(oid) AS size FROM pg_database; + EXEC SQL OPEN cur1; + + /* when end of result set reached, break out of while loop */ + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + /* Fetch multiple columns into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :dbval; + + /* Print members of the structure. */ + printf("oid=%d, datname=%s, size=%lld\n", dbval.oid, dbval.datname, dbval.size); + } + + EXEC SQL CLOSE cur1; + + + + + This example shows following result. (The exact values depend on + local circumstances.) + +oid=1, datname=template1, size=4324580 +oid=11510, datname=template0, size=4243460 +oid=11511, datname=postgres, size=4324580 +oid=313780, datname=testdb, size=8183012 + + + + + Structure host variables absorb as many columns + as the structure as fields. Additional columns can be assigned + to other host variables. For example, the above program could + also be restructured like this, with the size + variable outside the structure: + +EXEC SQL BEGIN DECLARE SECTION; + typedef struct + { + int oid; + char datname[65]; + } dbinfo_t; + + dbinfo_t dbval; + long long int size; +EXEC SQL END DECLARE SECTION; + + memset(&dbval, 0, sizeof(dbinfo_t)); + + EXEC SQL DECLARE cur1 CURSOR FOR SELECT oid, datname, pg_database_size(oid) AS size FROM pg_database; + EXEC SQL OPEN cur1; + + /* when end of result set reached, break out of while loop */ + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + /* Fetch multiple columns into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :dbval, :size; + + /* Print members of the structure. */ + printf("oid=%d, datname=%s, size=%lld\n", dbval.oid, dbval.datname, size); + } + + EXEC SQL CLOSE cur1; + + + + + + Typedefs + + + Use the typedef keyword to map new types to already + existing types. + +EXEC SQL BEGIN DECLARE SECTION; + typedef char mychartype[40]; + typedef long serial_t; +EXEC SQL END DECLARE SECTION; + + Note that you could also use: + +EXEC SQL TYPE serial_t IS long; + + This declaration does not need to be part of a declare section. + + + + + Pointers + + + You can declare pointers to the most common types. Note however + that you cannot use pointers as target variables of queries + without auto-allocation. See + for more information on auto-allocation. + + + + +EXEC SQL BEGIN DECLARE SECTION; + int *intp; + char **charp; +EXEC SQL END DECLARE SECTION; + + + + + + + + Handling Nonprimitive SQL Data Types + + + This section contains information on how to handle nonscalar and + user-defined SQL-level data types in ECPG applications. Note that + this is distinct from the handling of host variables of + nonprimitive types, described in the previous section. + + + + Arrays + + + Multi-dimensional SQL-level arrays are not directly supported in ECPG. + One-dimensional SQL-level arrays can be mapped into C array host + variables and vice-versa. However, when creating a statement ecpg does + not know the types of the columns, so that it cannot check if a C array + is input into a corresponding SQL-level array. When processing the + output of a SQL statement, ecpg has the necessary information and thus + checks if both are arrays. + + + + If a query accesses elements of an array + separately, then this avoids the use of arrays in ECPG. Then, a + host variable with a type that can be mapped to the element type + should be used. For example, if a column type is array of + integer, a host variable of type int + can be used. Also if the element type is varchar + or text, a host variable of type char[] + or VARCHAR[] can be used. + + + + Here is an example. Assume the following table: + +CREATE TABLE t3 ( + ii integer[] +); + +testdb=> SELECT * FROM t3; + ii +------------- + {1,2,3,4,5} +(1 row) + + + The following example program retrieves the 4th element of the + array and stores it into a host variable of + type int: + +EXEC SQL BEGIN DECLARE SECTION; +int ii; +EXEC SQL END DECLARE SECTION; + +EXEC SQL DECLARE cur1 CURSOR FOR SELECT ii[4] FROM t3; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH FROM cur1 INTO :ii ; + printf("ii=%d\n", ii); +} + +EXEC SQL CLOSE cur1; + + + This example shows the following result: + +ii=4 + + + + + To map multiple array elements to the multiple elements in an + array type host variables each element of array column and each + element of the host variable array have to be managed separately, + for example: + +EXEC SQL BEGIN DECLARE SECTION; +int ii_a[8]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL DECLARE cur1 CURSOR FOR SELECT ii[1], ii[2], ii[3], ii[4] FROM t3; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH FROM cur1 INTO :ii_a[0], :ii_a[1], :ii_a[2], :ii_a[3]; + ... +} + + + + + Note again that + +EXEC SQL BEGIN DECLARE SECTION; +int ii_a[8]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL DECLARE cur1 CURSOR FOR SELECT ii FROM t3; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* WRONG */ + EXEC SQL FETCH FROM cur1 INTO :ii_a; + ... +} + + would not work correctly in this case, because you cannot map an + array type column to an array host variable directly. + + + + Another workaround is to store arrays in their external string + representation in host variables of type char[] + or VARCHAR[]. For more details about this + representation, see . Note that + this means that the array cannot be accessed naturally as an + array in the host program (without further processing that parses + the text representation). + + + + + Composite Types + + + Composite types are not directly supported in ECPG, but an easy workaround is possible. + The + available workarounds are similar to the ones described for + arrays above: Either access each attribute separately or use the + external string representation. + + + + For the following examples, assume the following type and table: + +CREATE TYPE comp_t AS (intval integer, textval varchar(32)); +CREATE TABLE t4 (compval comp_t); +INSERT INTO t4 VALUES ( (256, 'PostgreSQL') ); + + + The most obvious solution is to access each attribute separately. + The following program retrieves data from the example table by + selecting each attribute of the type comp_t + separately: + +EXEC SQL BEGIN DECLARE SECTION; +int intval; +varchar textval[33]; +EXEC SQL END DECLARE SECTION; + +/* Put each element of the composite type column in the SELECT list. */ +EXEC SQL DECLARE cur1 CURSOR FOR SELECT (compval).intval, (compval).textval FROM t4; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* Fetch each element of the composite type column into host variables. */ + EXEC SQL FETCH FROM cur1 INTO :intval, :textval; + + printf("intval=%d, textval=%s\n", intval, textval.arr); +} + +EXEC SQL CLOSE cur1; + + + + + To enhance this example, the host variables to store values in + the FETCH command can be gathered into one + structure. For more details about the host variable in the + structure form, see . + To switch to the structure, the example can be modified as below. + The two host variables, intval + and textval, become members of + the comp_t structure, and the structure + is specified on the FETCH command. + +EXEC SQL BEGIN DECLARE SECTION; +typedef struct +{ + int intval; + varchar textval[33]; +} comp_t; + +comp_t compval; +EXEC SQL END DECLARE SECTION; + +/* Put each element of the composite type column in the SELECT list. */ +EXEC SQL DECLARE cur1 CURSOR FOR SELECT (compval).intval, (compval).textval FROM t4; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* Put all values in the SELECT list into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :compval; + + printf("intval=%d, textval=%s\n", compval.intval, compval.textval.arr); +} + +EXEC SQL CLOSE cur1; + + + Although a structure is used in the FETCH + command, the attribute names in the SELECT + clause are specified one by one. This can be enhanced by using + a * to ask for all attributes of the composite + type value. + +... +EXEC SQL DECLARE cur1 CURSOR FOR SELECT (compval).* FROM t4; +EXEC SQL OPEN cur1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + /* Put all values in the SELECT list into one structure. */ + EXEC SQL FETCH FROM cur1 INTO :compval; + + printf("intval=%d, textval=%s\n", compval.intval, compval.textval.arr); +} +... + + This way, composite types can be mapped into structures almost + seamlessly, even though ECPG does not understand the composite + type itself. + + + + Finally, it is also possible to store composite type values in + their external string representation in host variables of + type char[] or VARCHAR[]. But that + way, it is not easily possible to access the fields of the value + from the host program. + + + + + User-Defined Base Types + + + New user-defined base types are not directly supported by ECPG. + You can use the external string representation and host variables + of type char[] or VARCHAR[], and this + solution is indeed appropriate and sufficient for many types. + + + + Here is an example using the data type complex from + the example in . The external string + representation of that type is (%f,%f), + which is defined in the + functions complex_in() + and complex_out() functions + in . The following example inserts the + complex type values (1,1) + and (3,3) into the + columns a and b, and select + them from the table after that. + + +EXEC SQL BEGIN DECLARE SECTION; + varchar a[64]; + varchar b[64]; +EXEC SQL END DECLARE SECTION; + + EXEC SQL INSERT INTO test_complex VALUES ('(1,1)', '(3,3)'); + + EXEC SQL DECLARE cur1 CURSOR FOR SELECT a, b FROM test_complex; + EXEC SQL OPEN cur1; + + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + EXEC SQL FETCH FROM cur1 INTO :a, :b; + printf("a=%s, b=%s\n", a.arr, b.arr); + } + + EXEC SQL CLOSE cur1; + + + This example shows following result: + +a=(1,1), b=(3,3) + + + + + Another workaround is avoiding the direct use of the user-defined + types in ECPG and instead create a function or cast that converts + between the user-defined type and a primitive type that ECPG can + handle. Note, however, that type casts, especially implicit + ones, should be introduced into the type system very carefully. + + + + For example, + +CREATE FUNCTION create_complex(r double, i double) RETURNS complex +LANGUAGE SQL +IMMUTABLE +AS $$ SELECT $1 * complex '(1,0')' + $2 * complex '(0,1)' $$; + + After this definition, the following + +EXEC SQL BEGIN DECLARE SECTION; +double a, b, c, d; +EXEC SQL END DECLARE SECTION; + +a = 1; +b = 2; +c = 3; +d = 4; + +EXEC SQL INSERT INTO test_complex VALUES (create_complex(:a, :b), create_complex(:c, :d)); + + has the same effect as + +EXEC SQL INSERT INTO test_complex VALUES ('(1,2)', '(3,4)'); + + + + + + + Indicators + + + The examples above do not handle null values. In fact, the + retrieval examples will raise an error if they fetch a null value + from the database. To be able to pass null values to the database + or retrieve null values from the database, you need to append a + second host variable specification to each host variable that + contains data. This second host variable is called the + indicator and contains a flag that tells + whether the datum is null, in which case the value of the real + host variable is ignored. Here is an example that handles the + retrieval of null values correctly: + +EXEC SQL BEGIN DECLARE SECTION; +VARCHAR val; +int val_ind; +EXEC SQL END DECLARE SECTION: + + ... + +EXEC SQL SELECT b INTO :val :val_ind FROM test1; + + The indicator variable val_ind will be zero if + the value was not null, and it will be negative if the value was + null. + + + + The indicator has another function: if the indicator value is + positive, it means that the value is not null, but it was + truncated when it was stored in the host variable. + + + + If the argument -r no_indicator is passed to + the preprocessor ecpg, it works in + no-indicator mode. In no-indicator mode, if no + indicator variable is specified, null values are signaled (on + input and output) for character string types as empty string and + for integer types as the lowest possible value for type (for + example, INT_MIN for int). + + + + + + Dynamic SQL + + + In many cases, the particular SQL statements that an application + has to execute are known at the time the application is written. + In some cases, however, the SQL statements are composed at run time + or provided by an external source. In these cases you cannot embed + the SQL statements directly into the C source code, but there is a + facility that allows you to call arbitrary SQL statements that you + provide in a string variable. + + + + Executing Statements without a Result Set + + + The simplest way to execute an arbitrary SQL statement is to use + the command EXECUTE IMMEDIATE. For example: + +EXEC SQL BEGIN DECLARE SECTION; +const char *stmt = "CREATE TABLE test1 (...);"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL EXECUTE IMMEDIATE :stmt; + + EXECUTE IMMEDIATE can be used for SQL + statements that do not return a result set (e.g., + DDL, INSERT, UPDATE, + DELETE). You cannot execute statements that + retrieve data (e.g., SELECT) this way. The + next section describes how to do that. + + + + + Executing a Statement with Input Parameters + + + A more powerful way to execute arbitrary SQL statements is to + prepare them once and execute the prepared statement as often as + you like. It is also possible to prepare a generalized version of + a statement and then execute specific versions of it by + substituting parameters. When preparing the statement, write + question marks where you want to substitute parameters later. For + example: + +EXEC SQL BEGIN DECLARE SECTION; +const char *stmt = "INSERT INTO test1 VALUES(?, ?);"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE mystmt FROM :stmt; + ... +EXEC SQL EXECUTE mystmt USING 42, 'foobar'; + + + + + When you don't need the prepared statement anymore, you should + deallocate it: + +EXEC SQL DEALLOCATE PREPARE name; + + + + + + Executing a Statement with a Result Set + + + To execute an SQL statement with a single result row, + EXECUTE can be used. To save the result, add + an INTO clause. + ?"; +int v1, v2; +VARCHAR v3[50]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE mystmt FROM :stmt; + ... +EXEC SQL EXECUTE mystmt INTO :v1, :v2, :v3 USING 37; +]]> + + An EXECUTE command can have an + INTO clause, a USING clause, + both, or neither. + + + + If a query is expected to return more than one result row, a + cursor should be used, as in the following example. + (See for more details about the + cursor.) + +EXEC SQL BEGIN DECLARE SECTION; +char dbaname[128]; +char datname[128]; +char *stmt = "SELECT u.usename as dbaname, d.datname " + " FROM pg_database d, pg_user u " + " WHERE d.datdba = u.usesysid"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL CONNECT TO testdb AS con1 USER testuser; +EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + +EXEC SQL PREPARE stmt1 FROM :stmt; + +EXEC SQL DECLARE cursor1 CURSOR FOR stmt1; +EXEC SQL OPEN cursor1; + +EXEC SQL WHENEVER NOT FOUND DO BREAK; + +while (1) +{ + EXEC SQL FETCH cursor1 INTO :dbaname,:datname; + printf("dbaname=%s, datname=%s\n", dbaname, datname); +} + +EXEC SQL CLOSE cursor1; + +EXEC SQL COMMIT; +EXEC SQL DISCONNECT ALL; + + + + + + + pgtypes Library + + + The pgtypes library maps PostgreSQL database + types to C equivalents that can be used in C programs. It also offers + functions to do basic calculations with those types within C, i.e., without + the help of the PostgreSQL server. See the + following example: + + + + + + Character Strings + + Some functions such as PGTYPESnumeric_to_asc return + a pointer to a freshly allocated character string. These results should be + freed with PGTYPESchar_free instead of + free. (This is important only on Windows, where + memory allocation and release sometimes need to be done by the same + library.) + + + + + The numeric Type + + The numeric type offers to do calculations with arbitrary precision. See + for the equivalent type in the + PostgreSQL server. Because of the arbitrary precision this + variable needs to be able to expand and shrink dynamically. That's why you + can only create numeric variables on the heap, by means of the + PGTYPESnumeric_new and PGTYPESnumeric_free + functions. The decimal type, which is similar but limited in precision, + can be created on the stack as well as on the heap. + + + The following functions can be used to work with the numeric type: + + + PGTYPESnumeric_new + + + Request a pointer to a newly allocated numeric variable. + +numeric *PGTYPESnumeric_new(void); + + + + + + + PGTYPESnumeric_free + + + Free a numeric type, release all of its memory. + +void PGTYPESnumeric_free(numeric *var); + + + + + + + PGTYPESnumeric_from_asc + + + Parse a numeric type from its string notation. + +numeric *PGTYPESnumeric_from_asc(char *str, char **endptr); + + Valid formats are for example: + -2, + .794, + +3.44, + 592.49E07 or + -32.84e-4. + If the value could be parsed successfully, a valid pointer is returned, + else the NULL pointer. At the moment ECPG always parses the complete + string and so it currently does not support to store the address of the + first invalid character in *endptr. You can safely + set endptr to NULL. + + + + + + PGTYPESnumeric_to_asc + + + Returns a pointer to a string allocated by malloc that contains the string + representation of the numeric type num. + +char *PGTYPESnumeric_to_asc(numeric *num, int dscale); + + The numeric value will be printed with dscale decimal + digits, with rounding applied if necessary. + The result must be freed with PGTYPESchar_free(). + + + + + + PGTYPESnumeric_add + + + Add two numeric variables into a third one. + +int PGTYPESnumeric_add(numeric *var1, numeric *var2, numeric *result); + + The function adds the variables var1 and + var2 into the result variable + result. + The function returns 0 on success and -1 in case of error. + + + + + + PGTYPESnumeric_sub + + + Subtract two numeric variables and return the result in a third one. + +int PGTYPESnumeric_sub(numeric *var1, numeric *var2, numeric *result); + + The function subtracts the variable var2 from + the variable var1. The result of the operation is + stored in the variable result. + The function returns 0 on success and -1 in case of error. + + + + + + PGTYPESnumeric_mul + + + Multiply two numeric variables and return the result in a third one. + +int PGTYPESnumeric_mul(numeric *var1, numeric *var2, numeric *result); + + The function multiplies the variables var1 and + var2. The result of the operation is stored in the + variable result. + The function returns 0 on success and -1 in case of error. + + + + + + PGTYPESnumeric_div + + + Divide two numeric variables and return the result in a third one. + +int PGTYPESnumeric_div(numeric *var1, numeric *var2, numeric *result); + + The function divides the variables var1 by + var2. The result of the operation is stored in the + variable result. + The function returns 0 on success and -1 in case of error. + + + + + + PGTYPESnumeric_cmp + + + Compare two numeric variables. + +int PGTYPESnumeric_cmp(numeric *var1, numeric *var2) + + This function compares two numeric variables. In case of error, + INT_MAX is returned. On success, the function + returns one of three possible results: + + + + 1, if var1 is bigger than var2 + + + + + -1, if var1 is smaller than var2 + + + + + 0, if var1 and var2 are equal + + + + + + + + + PGTYPESnumeric_from_int + + + Convert an int variable to a numeric variable. + +int PGTYPESnumeric_from_int(signed int int_val, numeric *var); + + This function accepts a variable of type signed int and stores it + in the numeric variable var. Upon success, 0 is returned and + -1 in case of a failure. + + + + + + PGTYPESnumeric_from_long + + + Convert a long int variable to a numeric variable. + +int PGTYPESnumeric_from_long(signed long int long_val, numeric *var); + + This function accepts a variable of type signed long int and stores it + in the numeric variable var. Upon success, 0 is returned and + -1 in case of a failure. + + + + + + PGTYPESnumeric_copy + + + Copy over one numeric variable into another one. + +int PGTYPESnumeric_copy(numeric *src, numeric *dst); + + This function copies over the value of the variable that + src points to into the variable that dst + points to. It returns 0 on success and -1 if an error occurs. + + + + + + PGTYPESnumeric_from_double + + + Convert a variable of type double to a numeric. + +int PGTYPESnumeric_from_double(double d, numeric *dst); + + This function accepts a variable of type double and stores the result + in the variable that dst points to. It returns 0 on success + and -1 if an error occurs. + + + + + + PGTYPESnumeric_to_double + + + Convert a variable of type numeric to double. + +int PGTYPESnumeric_to_double(numeric *nv, double *dp) + + The function converts the numeric value from the variable that + nv points to into the double variable that dp points + to. It returns 0 on success and -1 if an error occurs, including + overflow. On overflow, the global variable errno will be set + to PGTYPES_NUM_OVERFLOW additionally. + + + + + + PGTYPESnumeric_to_int + + + Convert a variable of type numeric to int. + +int PGTYPESnumeric_to_int(numeric *nv, int *ip); + + The function converts the numeric value from the variable that + nv points to into the integer variable that ip + points to. It returns 0 on success and -1 if an error occurs, including + overflow. On overflow, the global variable errno will be set + to PGTYPES_NUM_OVERFLOW additionally. + + + + + + PGTYPESnumeric_to_long + + + Convert a variable of type numeric to long. + +int PGTYPESnumeric_to_long(numeric *nv, long *lp); + + The function converts the numeric value from the variable that + nv points to into the long integer variable that + lp points to. It returns 0 on success and -1 if an error + occurs, including overflow. On overflow, the global variable + errno will be set to PGTYPES_NUM_OVERFLOW + additionally. + + + + + + PGTYPESnumeric_to_decimal + + + Convert a variable of type numeric to decimal. + +int PGTYPESnumeric_to_decimal(numeric *src, decimal *dst); + + The function converts the numeric value from the variable that + src points to into the decimal variable that + dst points to. It returns 0 on success and -1 if an error + occurs, including overflow. On overflow, the global variable + errno will be set to PGTYPES_NUM_OVERFLOW + additionally. + + + + + + PGTYPESnumeric_from_decimal + + + Convert a variable of type decimal to numeric. + +int PGTYPESnumeric_from_decimal(decimal *src, numeric *dst); + + The function converts the decimal value from the variable that + src points to into the numeric variable that + dst points to. It returns 0 on success and -1 if an error + occurs. Since the decimal type is implemented as a limited version of + the numeric type, overflow cannot occur with this conversion. + + + + + + + + + The date Type + + The date type in C enables your programs to deal with data of the SQL type + date. See for the equivalent type in the + PostgreSQL server. + + + The following functions can be used to work with the date type: + + + PGTYPESdate_from_timestamp + + + Extract the date part from a timestamp. + +date PGTYPESdate_from_timestamp(timestamp dt); + + The function receives a timestamp as its only argument and returns the + extracted date part from this timestamp. + + + + + + PGTYPESdate_from_asc + + + Parse a date from its textual representation. + +date PGTYPESdate_from_asc(char *str, char **endptr); + + The function receives a C char* string str and a pointer to + a C char* string endptr. At the moment ECPG always parses + the complete string and so it currently does not support to store the + address of the first invalid character in *endptr. + You can safely set endptr to NULL. + + + Note that the function always assumes MDY-formatted dates and there is + currently no variable to change that within ECPG. + + + shows the allowed input formats. + + + Valid Input Formats for <function>PGTYPESdate_from_asc</function> + + + + Input + Result + + + + + January 8, 1999 + January 8, 1999 + + + 1999-01-08 + January 8, 1999 + + + 1/8/1999 + January 8, 1999 + + + 1/18/1999 + January 18, 1999 + + + 01/02/03 + February 1, 2003 + + + 1999-Jan-08 + January 8, 1999 + + + Jan-08-1999 + January 8, 1999 + + + 08-Jan-1999 + January 8, 1999 + + + 99-Jan-08 + January 8, 1999 + + + 08-Jan-99 + January 8, 1999 + + + 08-Jan-06 + January 8, 2006 + + + Jan-08-99 + January 8, 1999 + + + 19990108 + ISO 8601; January 8, 1999 + + + 990108 + ISO 8601; January 8, 1999 + + + 1999.008 + year and day of year + + + J2451187 + Julian day + + + January 8, 99 BC + year 99 before the Common Era + + + +
+ + + + + PGTYPESdate_to_asc + + + Return the textual representation of a date variable. + +char *PGTYPESdate_to_asc(date dDate); + + The function receives the date dDate as its only parameter. + It will output the date in the form 1999-01-18, i.e., in the + YYYY-MM-DD format. + The result must be freed with PGTYPESchar_free(). + + + + + + PGTYPESdate_julmdy + + + Extract the values for the day, the month and the year from a variable + of type date. + +void PGTYPESdate_julmdy(date d, int *mdy); + + + The function receives the date d and a pointer to an array + of 3 integer values mdy. The variable name indicates + the sequential order: mdy[0] will be set to contain the + number of the month, mdy[1] will be set to the value of the + day and mdy[2] will contain the year. + + + + + + PGTYPESdate_mdyjul + + + Create a date value from an array of 3 integers that specify the + day, the month and the year of the date. + +void PGTYPESdate_mdyjul(int *mdy, date *jdate); + + The function receives the array of the 3 integers (mdy) as + its first argument and as its second argument a pointer to a variable + of type date that should hold the result of the operation. + + + + + + PGTYPESdate_dayofweek + + + Return a number representing the day of the week for a date value. + +int PGTYPESdate_dayofweek(date d); + + The function receives the date variable d as its only + argument and returns an integer that indicates the day of the week for + this date. + + + + 0 - Sunday + + + + + 1 - Monday + + + + + 2 - Tuesday + + + + + 3 - Wednesday + + + + + 4 - Thursday + + + + + 5 - Friday + + + + + 6 - Saturday + + + + + + + + + PGTYPESdate_today + + + Get the current date. + +void PGTYPESdate_today(date *d); + + The function receives a pointer to a date variable (d) + that it sets to the current date. + + + + + + PGTYPESdate_fmt_asc + + + Convert a variable of type date to its textual representation using a + format mask. + +int PGTYPESdate_fmt_asc(date dDate, char *fmtstring, char *outbuf); + + The function receives the date to convert (dDate), the + format mask (fmtstring) and the string that will hold the + textual representation of the date (outbuf). + + + On success, 0 is returned and a negative value if an error occurred. + + + The following literals are the field specifiers you can use: + + + + dd - The number of the day of the month. + + + + + mm - The number of the month of the year. + + + + + yy - The number of the year as a two digit number. + + + + + yyyy - The number of the year as a four digit number. + + + + + ddd - The name of the day (abbreviated). + + + + + mmm - The name of the month (abbreviated). + + + + All other characters are copied 1:1 to the output string. + + + indicates a few possible formats. This will give + you an idea of how to use this function. All output lines are based on + the same date: November 23, 1959. + + + Valid Input Formats for <function>PGTYPESdate_fmt_asc</function> + + + + Format + Result + + + + + mmddyy + 112359 + + + ddmmyy + 231159 + + + yymmdd + 591123 + + + yy/mm/dd + 59/11/23 + + + yy mm dd + 59 11 23 + + + yy.mm.dd + 59.11.23 + + + .mm.yyyy.dd. + .11.1959.23. + + + mmm. dd, yyyy + Nov. 23, 1959 + + + mmm dd yyyy + Nov 23 1959 + + + yyyy dd mm + 1959 23 11 + + + ddd, mmm. dd, yyyy + Mon, Nov. 23, 1959 + + + (ddd) mmm. dd, yyyy + (Mon) Nov. 23, 1959 + + + +
+ + + + + PGTYPESdate_defmt_asc + + + Use a format mask to convert a C char* string to a value of type + date. + +int PGTYPESdate_defmt_asc(date *d, char *fmt, char *str); + + + The function receives a pointer to the date value that should hold the + result of the operation (d), the format mask to use for + parsing the date (fmt) and the C char* string containing + the textual representation of the date (str). The textual + representation is expected to match the format mask. However you do not + need to have a 1:1 mapping of the string to the format mask. The + function only analyzes the sequential order and looks for the literals + yy or yyyy that indicate the + position of the year, mm to indicate the position of + the month and dd to indicate the position of the + day. + + + indicates a few possible formats. This will give + you an idea of how to use this function. + + + Valid Input Formats for <function>rdefmtdate</function> + + + + Format + String + Result + + + + + ddmmyy + 21-2-54 + 1954-02-21 + + + ddmmyy + 2-12-54 + 1954-12-02 + + + ddmmyy + 20111954 + 1954-11-20 + + + ddmmyy + 130464 + 1964-04-13 + + + mmm.dd.yyyy + MAR-12-1967 + 1967-03-12 + + + yy/mm/dd + 1954, February 3rd + 1954-02-03 + + + mmm.dd.yyyy + 041269 + 1969-04-12 + + + yy/mm/dd + In the year 2525, in the month of July, mankind will be alive on the 28th day + 2525-07-28 + + + dd-mm-yy + I said on the 28th of July in the year 2525 + 2525-07-28 + + + mmm.dd.yyyy + 9/14/58 + 1958-09-14 + + + yy/mm/dd + 47/03/29 + 1947-03-29 + + + mmm.dd.yyyy + oct 28 1975 + 1975-10-28 + + + mmddyy + Nov 14th, 1985 + 1985-11-14 + + + +
+ + + + + + + + The timestamp Type + + The timestamp type in C enables your programs to deal with data of the SQL + type timestamp. See for the equivalent + type in the PostgreSQL server. + + + The following functions can be used to work with the timestamp type: + + + PGTYPEStimestamp_from_asc + + + Parse a timestamp from its textual representation into a timestamp + variable. + +timestamp PGTYPEStimestamp_from_asc(char *str, char **endptr); + + The function receives the string to parse (str) and a + pointer to a C char* (endptr). + At the moment ECPG always parses + the complete string and so it currently does not support to store the + address of the first invalid character in *endptr. + You can safely set endptr to NULL. + + + The function returns the parsed timestamp on success. On error, + PGTYPESInvalidTimestamp is returned and errno is + set to PGTYPES_TS_BAD_TIMESTAMP. See for important notes on this value. + + + In general, the input string can contain any combination of an allowed + date specification, a whitespace character and an allowed time + specification. Note that time zones are not supported by ECPG. It can + parse them but does not apply any calculation as the + PostgreSQL server does for example. Timezone + specifiers are silently discarded. + + + contains a few examples for input strings. + + + Valid Input Formats for <function>PGTYPEStimestamp_from_asc</function> + + + + Input + Result + + + + + 1999-01-08 04:05:06 + 1999-01-08 04:05:06 + + + January 8 04:05:06 1999 PST + 1999-01-08 04:05:06 + + + 1999-Jan-08 04:05:06.789-8 + 1999-01-08 04:05:06.789 (time zone specifier ignored) + + + J2451187 04:05-08:00 + 1999-01-08 04:05:00 (time zone specifier ignored) + + + +
+ + + + + PGTYPEStimestamp_to_asc + + + Converts a date to a C char* string. + +char *PGTYPEStimestamp_to_asc(timestamp tstamp); + + The function receives the timestamp tstamp as + its only argument and returns an allocated string that contains the + textual representation of the timestamp. + The result must be freed with PGTYPESchar_free(). + + + + + + PGTYPEStimestamp_current + + + Retrieve the current timestamp. + +void PGTYPEStimestamp_current(timestamp *ts); + + The function retrieves the current timestamp and saves it into the + timestamp variable that ts points to. + + + + + + PGTYPEStimestamp_fmt_asc + + + Convert a timestamp variable to a C char* using a format mask. + +int PGTYPEStimestamp_fmt_asc(timestamp *ts, char *output, int str_len, char *fmtstr); + + The function receives a pointer to the timestamp to convert as its + first argument (ts), a pointer to the output buffer + (output), the maximal length that has been allocated for + the output buffer (str_len) and the format mask to + use for the conversion (fmtstr). + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + You can use the following format specifiers for the format mask. The + format specifiers are the same ones that are used in the + strftime function in libc. Any + non-format specifier will be copied into the output buffer. + + + + + %A - is replaced by national representation of + the full weekday name. + + + + + %a - is replaced by national representation of + the abbreviated weekday name. + + + + + %B - is replaced by national representation of + the full month name. + + + + + %b - is replaced by national representation of + the abbreviated month name. + + + + + %C - is replaced by (year / 100) as decimal + number; single digits are preceded by a zero. + + + + + %c - is replaced by national representation of + time and date. + + + + + %D - is equivalent to + %m/%d/%y. + + + + + %d - is replaced by the day of the month as a + decimal number (01–31). + + + + + %E* %O* - POSIX locale + extensions. The sequences + %Ec + %EC + %Ex + %EX + %Ey + %EY + %Od + %Oe + %OH + %OI + %Om + %OM + %OS + %Ou + %OU + %OV + %Ow + %OW + %Oy + are supposed to provide alternative representations. + + + Additionally %OB implemented to represent + alternative months names (used standalone, without day mentioned). + + + + + %e - is replaced by the day of month as a decimal + number (1–31); single digits are preceded by a blank. + + + + + %F - is equivalent to %Y-%m-%d. + + + + + %G - is replaced by a year as a decimal number + with century. This year is the one that contains the greater part of + the week (Monday as the first day of the week). + + + + + %g - is replaced by the same year as in + %G, but as a decimal number without century + (00–99). + + + + + %H - is replaced by the hour (24-hour clock) as a + decimal number (00–23). + + + + + %h - the same as %b. + + + + + %I - is replaced by the hour (12-hour clock) as a + decimal number (01–12). + + + + + %j - is replaced by the day of the year as a + decimal number (001–366). + + + + + %k - is replaced by the hour (24-hour clock) as a + decimal number (0–23); single digits are preceded by a blank. + + + + + %l - is replaced by the hour (12-hour clock) as a + decimal number (1–12); single digits are preceded by a blank. + + + + + %M - is replaced by the minute as a decimal + number (00–59). + + + + + %m - is replaced by the month as a decimal number + (01–12). + + + + + %n - is replaced by a newline. + + + + + %O* - the same as %E*. + + + + + %p - is replaced by national representation of + either ante meridiem or post meridiem as appropriate. + + + + + %R - is equivalent to %H:%M. + + + + + %r - is equivalent to %I:%M:%S + %p. + + + + + %S - is replaced by the second as a decimal + number (00–60). + + + + + %s - is replaced by the number of seconds since + the Epoch, UTC. + + + + + %T - is equivalent to %H:%M:%S + + + + + %t - is replaced by a tab. + + + + + %U - is replaced by the week number of the year + (Sunday as the first day of the week) as a decimal number (00–53). + + + + + %u - is replaced by the weekday (Monday as the + first day of the week) as a decimal number (1–7). + + + + + %V - is replaced by the week number of the year + (Monday as the first day of the week) as a decimal number (01–53). + If the week containing January 1 has four or more days in the new + year, then it is week 1; otherwise it is the last week of the + previous year, and the next week is week 1. + + + + + %v - is equivalent to + %e-%b-%Y. + + + + + %W - is replaced by the week number of the year + (Monday as the first day of the week) as a decimal number (00–53). + + + + + %w - is replaced by the weekday (Sunday as the + first day of the week) as a decimal number (0–6). + + + + + %X - is replaced by national representation of + the time. + + + + + %x - is replaced by national representation of + the date. + + + + + %Y - is replaced by the year with century as a + decimal number. + + + + + %y - is replaced by the year without century as a + decimal number (00–99). + + + + + %Z - is replaced by the time zone name. + + + + + %z - is replaced by the time zone offset from + UTC; a leading plus sign stands for east of UTC, a minus sign for + west of UTC, hours and minutes follow with two digits each and no + delimiter between them (common form for RFC 822 date headers). + + + + + %+ - is replaced by national representation of + the date and time. + + + + + %-* - GNU libc extension. Do not do any padding + when performing numerical outputs. + + + + + $_* - GNU libc extension. Explicitly specify space for padding. + + + + + %0* - GNU libc extension. Explicitly specify zero + for padding. + + + + + %% - is replaced by %. + + + + + + + + + PGTYPEStimestamp_sub + + + Subtract one timestamp from another one and save the result in a + variable of type interval. + +int PGTYPEStimestamp_sub(timestamp *ts1, timestamp *ts2, interval *iv); + + The function will subtract the timestamp variable that ts2 + points to from the timestamp variable that ts1 points to + and will store the result in the interval variable that iv + points to. + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + + + + PGTYPEStimestamp_defmt_asc + + + Parse a timestamp value from its textual representation using a + formatting mask. + +int PGTYPEStimestamp_defmt_asc(char *str, char *fmt, timestamp *d); + + The function receives the textual representation of a timestamp in the + variable str as well as the formatting mask to use in the + variable fmt. The result will be stored in the variable + that d points to. + + + If the formatting mask fmt is NULL, the function will fall + back to the default formatting mask which is %Y-%m-%d + %H:%M:%S. + + + This is the reverse function to . See the documentation there in + order to find out about the possible formatting mask entries. + + + + + + PGTYPEStimestamp_add_interval + + + Add an interval variable to a timestamp variable. + +int PGTYPEStimestamp_add_interval(timestamp *tin, interval *span, timestamp *tout); + + The function receives a pointer to a timestamp variable tin + and a pointer to an interval variable span. It adds the + interval to the timestamp and saves the resulting timestamp in the + variable that tout points to. + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + + + + PGTYPEStimestamp_sub_interval + + + Subtract an interval variable from a timestamp variable. + +int PGTYPEStimestamp_sub_interval(timestamp *tin, interval *span, timestamp *tout); + + The function subtracts the interval variable that span + points to from the timestamp variable that tin points to + and saves the result into the variable that tout points + to. + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + + + + + + + The interval Type + + The interval type in C enables your programs to deal with data of the SQL + type interval. See for the equivalent + type in the PostgreSQL server. + + + The following functions can be used to work with the interval type: + + + + PGTYPESinterval_new + + + Return a pointer to a newly allocated interval variable. + +interval *PGTYPESinterval_new(void); + + + + + + + PGTYPESinterval_free + + + Release the memory of a previously allocated interval variable. + +void PGTYPESinterval_free(interval *intvl); + + + + + + + PGTYPESinterval_from_asc + + + Parse an interval from its textual representation. + +interval *PGTYPESinterval_from_asc(char *str, char **endptr); + + The function parses the input string str and returns a + pointer to an allocated interval variable. + At the moment ECPG always parses + the complete string and so it currently does not support to store the + address of the first invalid character in *endptr. + You can safely set endptr to NULL. + + + + + + PGTYPESinterval_to_asc + + + Convert a variable of type interval to its textual representation. + +char *PGTYPESinterval_to_asc(interval *span); + + The function converts the interval variable that span + points to into a C char*. The output looks like this example: + @ 1 day 12 hours 59 mins 10 secs. + The result must be freed with PGTYPESchar_free(). + + + + + + PGTYPESinterval_copy + + + Copy a variable of type interval. + +int PGTYPESinterval_copy(interval *intvlsrc, interval *intvldest); + + The function copies the interval variable that intvlsrc + points to into the variable that intvldest points to. Note + that you need to allocate the memory for the destination variable + before. + + + + + + + + + The decimal Type + + The decimal type is similar to the numeric type. However it is limited to + a maximum precision of 30 significant digits. In contrast to the numeric + type which can be created on the heap only, the decimal type can be + created either on the stack or on the heap (by means of the functions + PGTYPESdecimal_new and + PGTYPESdecimal_free). + There are a lot of other functions that deal with the decimal type in the + Informix compatibility mode described in . + + + The following functions can be used to work with the decimal type and are + not only contained in the libcompat library. + + + PGTYPESdecimal_new + + + Request a pointer to a newly allocated decimal variable. + +decimal *PGTYPESdecimal_new(void); + + + + + + + PGTYPESdecimal_free + + + Free a decimal type, release all of its memory. + +void PGTYPESdecimal_free(decimal *var); + + + + + + + + + + errno Values of pgtypeslib + + + + PGTYPES_NUM_BAD_NUMERIC + + + An argument should contain a numeric variable (or point to a numeric + variable) but in fact its in-memory representation was invalid. + + + + + + PGTYPES_NUM_OVERFLOW + + + An overflow occurred. Since the numeric type can deal with almost + arbitrary precision, converting a numeric variable into other types + might cause overflow. + + + + + + PGTYPES_NUM_UNDERFLOW + + + An underflow occurred. Since the numeric type can deal with almost + arbitrary precision, converting a numeric variable into other types + might cause underflow. + + + + + + PGTYPES_NUM_DIVIDE_ZERO + + + A division by zero has been attempted. + + + + + + PGTYPES_DATE_BAD_DATE + + + An invalid date string was passed to + the PGTYPESdate_from_asc function. + + + + + + PGTYPES_DATE_ERR_EARGS + + + Invalid arguments were passed to the + PGTYPESdate_defmt_asc function. + + + + + + PGTYPES_DATE_ERR_ENOSHORTDATE + + + An invalid token in the input string was found by the + PGTYPESdate_defmt_asc function. + + + + + + PGTYPES_INTVL_BAD_INTERVAL + + + An invalid interval string was passed to the + PGTYPESinterval_from_asc function, or an + invalid interval value was passed to the + PGTYPESinterval_to_asc function. + + + + + + PGTYPES_DATE_ERR_ENOTDMY + + + There was a mismatch in the day/month/year assignment in the + PGTYPESdate_defmt_asc function. + + + + + + PGTYPES_DATE_BAD_DAY + + + An invalid day of the month value was found by + the PGTYPESdate_defmt_asc function. + + + + + + PGTYPES_DATE_BAD_MONTH + + + An invalid month value was found by + the PGTYPESdate_defmt_asc function. + + + + + + PGTYPES_TS_BAD_TIMESTAMP + + + An invalid timestamp string pass passed to + the PGTYPEStimestamp_from_asc function, + or an invalid timestamp value was passed to + the PGTYPEStimestamp_to_asc function. + + + + + + PGTYPES_TS_ERR_EINFTIME + + + An infinite timestamp value was encountered in a context that + cannot handle it. + + + + + + + + + Special Constants of pgtypeslib + + + + PGTYPESInvalidTimestamp + + + A value of type timestamp representing an invalid time stamp. This is + returned by the function PGTYPEStimestamp_from_asc on + parse error. + Note that due to the internal representation of the timestamp data type, + PGTYPESInvalidTimestamp is also a valid timestamp at + the same time. It is set to 1899-12-31 23:59:59. In order + to detect errors, make sure that your application does not only test + for PGTYPESInvalidTimestamp but also for + errno != 0 after each call to + PGTYPEStimestamp_from_asc. + + + + + + + + + + Using Descriptor Areas + + + An SQL descriptor area is a more sophisticated method for processing + the result of a SELECT, FETCH or + a DESCRIBE statement. An SQL descriptor area groups + the data of one row of data together with metadata items into one + data structure. The metadata is particularly useful when executing + dynamic SQL statements, where the nature of the result columns might + not be known ahead of time. PostgreSQL provides two ways to use + Descriptor Areas: the named SQL Descriptor Areas and the C-structure + SQLDAs. + + + + Named SQL Descriptor Areas + + + A named SQL descriptor area consists of a header, which contains + information concerning the entire descriptor, and one or more item + descriptor areas, which basically each describe one column in the + result row. + + + + Before you can use an SQL descriptor area, you need to allocate one: + +EXEC SQL ALLOCATE DESCRIPTOR identifier; + + The identifier serves as the variable name of the + descriptor area. + When you don't need the descriptor anymore, you should deallocate + it: + +EXEC SQL DEALLOCATE DESCRIPTOR identifier; + + + + + To use a descriptor area, specify it as the storage target in an + INTO clause, instead of listing host variables: + +EXEC SQL FETCH NEXT FROM mycursor INTO SQL DESCRIPTOR mydesc; + + If the result set is empty, the Descriptor Area will still contain + the metadata from the query, i.e., the field names. + + + + For not yet executed prepared queries, the DESCRIBE + statement can be used to get the metadata of the result set: + +EXEC SQL BEGIN DECLARE SECTION; +char *sql_stmt = "SELECT * FROM table1"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE stmt1 FROM :sql_stmt; +EXEC SQL DESCRIBE stmt1 INTO SQL DESCRIPTOR mydesc; + + + + + Before PostgreSQL 9.0, the SQL keyword was optional, + so using DESCRIPTOR and SQL DESCRIPTOR + produced named SQL Descriptor Areas. Now it is mandatory, omitting + the SQL keyword produces SQLDA Descriptor Areas, + see . + + + + In DESCRIBE and FETCH statements, + the INTO and USING keywords can be + used to similarly: they produce the result set and the metadata in a + Descriptor Area. + + + + Now how do you get the data out of the descriptor area? You can + think of the descriptor area as a structure with named fields. To + retrieve the value of a field from the header and store it into a + host variable, use the following command: + +EXEC SQL GET DESCRIPTOR name :hostvar = field; + + Currently, there is only one header field defined: + COUNT, which tells how many item + descriptor areas exist (that is, how many columns are contained in + the result). The host variable needs to be of an integer type. To + get a field from the item descriptor area, use the following + command: + +EXEC SQL GET DESCRIPTOR name VALUE num :hostvar = field; + + num can be a literal integer or a host + variable containing an integer. Possible fields are: + + + + CARDINALITY (integer) + + + number of rows in the result set + + + + + + DATA + + + actual data item (therefore, the data type of this field + depends on the query) + + + + + + DATETIME_INTERVAL_CODE (integer) + + + When TYPE is 9, + DATETIME_INTERVAL_CODE will have a value of + 1 for DATE, + 2 for TIME, + 3 for TIMESTAMP, + 4 for TIME WITH TIME ZONE, or + 5 for TIMESTAMP WITH TIME ZONE. + + + + + + DATETIME_INTERVAL_PRECISION (integer) + + + not implemented + + + + + + INDICATOR (integer) + + + the indicator (indicating a null value or a value truncation) + + + + + + KEY_MEMBER (integer) + + + not implemented + + + + + + LENGTH (integer) + + + length of the datum in characters + + + + + + NAME (string) + + + name of the column + + + + + + NULLABLE (integer) + + + not implemented + + + + + + OCTET_LENGTH (integer) + + + length of the character representation of the datum in bytes + + + + + + PRECISION (integer) + + + precision (for type numeric) + + + + + + RETURNED_LENGTH (integer) + + + length of the datum in characters + + + + + + RETURNED_OCTET_LENGTH (integer) + + + length of the character representation of the datum in bytes + + + + + + SCALE (integer) + + + scale (for type numeric) + + + + + + TYPE (integer) + + + numeric code of the data type of the column + + + + + + + + In EXECUTE, DECLARE and OPEN + statements, the effect of the INTO and USING + keywords are different. A Descriptor Area can also be manually built to + provide the input parameters for a query or a cursor and + USING SQL DESCRIPTOR name + is the way to pass the input parameters into a parameterized query. The statement + to build a named SQL Descriptor Area is below: + +EXEC SQL SET DESCRIPTOR name VALUE num field = :hostvar; + + + + + PostgreSQL supports retrieving more that one record in one FETCH + statement and storing the data in host variables in this case assumes that the + variable is an array. E.g.: + +EXEC SQL BEGIN DECLARE SECTION; +int id[5]; +EXEC SQL END DECLARE SECTION; + +EXEC SQL FETCH 5 FROM mycursor INTO SQL DESCRIPTOR mydesc; + +EXEC SQL GET DESCRIPTOR mydesc VALUE 1 :id = DATA; + + + + + + + + SQLDA Descriptor Areas + + + An SQLDA Descriptor Area is a C language structure which can be also used + to get the result set and the metadata of a query. One structure stores one + record from the result set. + +EXEC SQL include sqlda.h; +sqlda_t *mysqlda; + +EXEC SQL FETCH 3 FROM mycursor INTO DESCRIPTOR mysqlda; + + Note that the SQL keyword is omitted. The paragraphs about + the use cases of the INTO and USING + keywords in also apply here with an addition. + In a DESCRIBE statement the DESCRIPTOR + keyword can be completely omitted if the INTO keyword is used: + +EXEC SQL DESCRIBE prepared_statement INTO mysqlda; + + + + + + The general flow of a program that uses SQLDA is: + + Prepare a query, and declare a cursor for it. + Declare an SQLDA for the result rows. + Declare an SQLDA for the input parameters, and initialize them (memory allocation, parameter settings). + Open a cursor with the input SQLDA. + Fetch rows from the cursor, and store them into an output SQLDA. + Read values from the output SQLDA into the host variables (with conversion if necessary). + Close the cursor. + Free the memory area allocated for the input SQLDA. + + + + SQLDA Data Structure + + + SQLDA uses three data structure + types: sqlda_t, sqlvar_t, + and struct sqlname. + + + + + PostgreSQL's SQLDA has a similar data structure to the one in + IBM DB2 Universal Database, so some technical information on + DB2's SQLDA could help understanding PostgreSQL's one better. + + + + + sqlda_t Structure + + + The structure type sqlda_t is the type of the + actual SQLDA. It holds one record. And two or + more sqlda_t structures can be connected in a + linked list with the pointer in + the desc_next field, thus + representing an ordered collection of rows. So, when two or + more rows are fetched, the application can read them by + following the desc_next pointer in + each sqlda_t node. + + + + The definition of sqlda_t is: + +struct sqlda_struct +{ + char sqldaid[8]; + long sqldabc; + short sqln; + short sqld; + struct sqlda_struct *desc_next; + struct sqlvar_struct sqlvar[1]; +}; + +typedef struct sqlda_struct sqlda_t; + + + The meaning of the fields is: + + + + sqldaid + + + It contains the literal string "SQLDA ". + + + + + + sqldabc + + + It contains the size of the allocated space in bytes. + + + + + + sqln + + + It contains the number of input parameters for a parameterized query in + case it's passed into OPEN, DECLARE or + EXECUTE statements using the USING + keyword. In case it's used as output of SELECT, + EXECUTE or FETCH statements, + its value is the same as sqld + statement + + + + + + sqld + + + It contains the number of fields in a result set. + + + + + + desc_next + + + If the query returns more than one record, multiple linked + SQLDA structures are returned, and desc_next holds + a pointer to the next entry in the list. + + + + + sqlvar + + + This is the array of the columns in the result set. + + + + + + + + + sqlvar_t Structure + + + The structure type sqlvar_t holds a column value + and metadata such as type and length. The definition of the type + is: + + +struct sqlvar_struct +{ + short sqltype; + short sqllen; + char *sqldata; + short *sqlind; + struct sqlname sqlname; +}; + +typedef struct sqlvar_struct sqlvar_t; + + + The meaning of the fields is: + + + + sqltype + + + Contains the type identifier of the field. For values, + see enum ECPGttype in ecpgtype.h. + + + + + + sqllen + + + Contains the binary length of the field. e.g., 4 bytes for ECPGt_int. + + + + + + sqldata + + + Points to the data. The format of the data is described + in . + + + + + + sqlind + + + Points to the null indicator. 0 means not null, -1 means + null. + + + + + + sqlname + + + The name of the field. + + + + + + + + + struct sqlname Structure + + + A struct sqlname structure holds a column name. It + is used as a member of the sqlvar_t structure. The + definition of the structure is: + +#define NAMEDATALEN 64 + +struct sqlname +{ + short length; + char data[NAMEDATALEN]; +}; + + The meaning of the fields is: + + + length + + + Contains the length of the field name. + + + + + data + + + Contains the actual field name. + + + + + + + + + + Retrieving a Result Set Using an SQLDA + + + + The general steps to retrieve a query result set through an + SQLDA are: + + Declare an sqlda_t structure to receive the result set. + Execute FETCH/EXECUTE/DESCRIBE commands to process a query specifying the declared SQLDA. + Check the number of records in the result set by looking at sqln, a member of the sqlda_t structure. + Get the values of each column from sqlvar[0], sqlvar[1], etc., members of the sqlda_t structure. + Go to next row (sqlda_t structure) by following the desc_next pointer, a member of the sqlda_t structure. + Repeat above as you need. + + + + Here is an example retrieving a result set through an SQLDA. + + + + First, declare a sqlda_t structure to receive the result set. + +sqlda_t *sqlda1; + + + + + Next, specify the SQLDA in a command. This is + a FETCH command example. + +EXEC SQL FETCH NEXT FROM cur1 INTO DESCRIPTOR sqlda1; + + + + + Run a loop following the linked list to retrieve the rows. + +sqlda_t *cur_sqlda; + +for (cur_sqlda = sqlda1; + cur_sqlda != NULL; + cur_sqlda = cur_sqlda->desc_next) +{ + ... +} + + + + + Inside the loop, run another loop to retrieve each column data + (sqlvar_t structure) of the row. + +for (i = 0; i < cur_sqlda->sqld; i++) +{ + sqlvar_t v = cur_sqlda->sqlvar[i]; + char *sqldata = v.sqldata; + short sqllen = v.sqllen; + ... +} + + + + + To get a column value, check the sqltype value, + a member of the sqlvar_t structure. Then, switch + to an appropriate way, depending on the column type, to copy + data from the sqlvar field to a host variable. + +char var_buf[1024]; + +switch (v.sqltype) +{ + case ECPGt_char: + memset(&var_buf, 0, sizeof(var_buf)); + memcpy(&var_buf, sqldata, (sizeof(var_buf) <= sqllen ? sizeof(var_buf) - 1 : sqllen)); + break; + + case ECPGt_int: /* integer */ + memcpy(&intval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%d", intval); + break; + + ... +} + + + + + + Passing Query Parameters Using an SQLDA + + + + The general steps to use an SQLDA to pass input + parameters to a prepared query are: + + Create a prepared query (prepared statement) + Declare a sqlda_t structure as an input SQLDA. + Allocate memory area (as sqlda_t structure) for the input SQLDA. + Set (copy) input values in the allocated memory. + Open a cursor with specifying the input SQLDA. + + + + Here is an example. + + + + First, create a prepared statement. + +EXEC SQL BEGIN DECLARE SECTION; +char query[1024] = "SELECT d.oid, * FROM pg_database d, pg_stat_database s WHERE d.oid = s.datid AND (d.datname = ? OR d.oid = ?)"; +EXEC SQL END DECLARE SECTION; + +EXEC SQL PREPARE stmt1 FROM :query; + + + + + Next, allocate memory for an SQLDA, and set the number of input + parameters in sqln, a member variable of + the sqlda_t structure. When two or more input + parameters are required for the prepared query, the application + has to allocate additional memory space which is calculated by + (nr. of params - 1) * sizeof(sqlvar_t). The example shown here + allocates memory space for two input parameters. + +sqlda_t *sqlda2; + +sqlda2 = (sqlda_t *) malloc(sizeof(sqlda_t) + sizeof(sqlvar_t)); +memset(sqlda2, 0, sizeof(sqlda_t) + sizeof(sqlvar_t)); + +sqlda2->sqln = 2; /* number of input variables */ + + + + + After memory allocation, store the parameter values into the + sqlvar[] array. (This is same array used for + retrieving column values when the SQLDA is receiving a result + set.) In this example, the input parameters + are "postgres", having a string type, + and 1, having an integer type. + +sqlda2->sqlvar[0].sqltype = ECPGt_char; +sqlda2->sqlvar[0].sqldata = "postgres"; +sqlda2->sqlvar[0].sqllen = 8; + +int intval = 1; +sqlda2->sqlvar[1].sqltype = ECPGt_int; +sqlda2->sqlvar[1].sqldata = (char *) &intval; +sqlda2->sqlvar[1].sqllen = sizeof(intval); + + + + + By opening a cursor and specifying the SQLDA that was set up + beforehand, the input parameters are passed to the prepared + statement. + +EXEC SQL OPEN cur1 USING DESCRIPTOR sqlda2; + + + + + Finally, after using input SQLDAs, the allocated memory space + must be freed explicitly, unlike SQLDAs used for receiving query + results. + +free(sqlda2); + + + + + + A Sample Application Using SQLDA + + + Here is an example program, which describes how to fetch access + statistics of the databases, specified by the input parameters, + from the system catalogs. + + + + This application joins two system tables, pg_database and + pg_stat_database on the database OID, and also fetches and shows + the database statistics which are retrieved by two input + parameters (a database postgres, and OID 1). + + + + First, declare an SQLDA for input and an SQLDA for output. + +EXEC SQL include sqlda.h; + +sqlda_t *sqlda1; /* an output descriptor */ +sqlda_t *sqlda2; /* an input descriptor */ + + + + + Next, connect to the database, prepare a statement, and declare a + cursor for the prepared statement. + +int +main(void) +{ + EXEC SQL BEGIN DECLARE SECTION; + char query[1024] = "SELECT d.oid,* FROM pg_database d, pg_stat_database s WHERE d.oid=s.datid AND ( d.datname=? OR d.oid=? )"; + EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb AS con1 USER testuser; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + EXEC SQL PREPARE stmt1 FROM :query; + EXEC SQL DECLARE cur1 CURSOR FOR stmt1; + + + + + Next, put some values in the input SQLDA for the input + parameters. Allocate memory for the input SQLDA, and set the + number of input parameters to sqln. Store + type, value, and value length into sqltype, + sqldata, and sqllen in the + sqlvar structure. + + + /* Create SQLDA structure for input parameters. */ + sqlda2 = (sqlda_t *) malloc(sizeof(sqlda_t) + sizeof(sqlvar_t)); + memset(sqlda2, 0, sizeof(sqlda_t) + sizeof(sqlvar_t)); + sqlda2->sqln = 2; /* number of input variables */ + + sqlda2->sqlvar[0].sqltype = ECPGt_char; + sqlda2->sqlvar[0].sqldata = "postgres"; + sqlda2->sqlvar[0].sqllen = 8; + + intval = 1; + sqlda2->sqlvar[1].sqltype = ECPGt_int; + sqlda2->sqlvar[1].sqldata = (char *)&intval; + sqlda2->sqlvar[1].sqllen = sizeof(intval); + + + + + After setting up the input SQLDA, open a cursor with the input + SQLDA. + + + /* Open a cursor with input parameters. */ + EXEC SQL OPEN cur1 USING DESCRIPTOR sqlda2; + + + + + Fetch rows into the output SQLDA from the opened cursor. + (Generally, you have to call FETCH repeatedly + in the loop, to fetch all rows in the result set.) + + while (1) + { + sqlda_t *cur_sqlda; + + /* Assign descriptor to the cursor */ + EXEC SQL FETCH NEXT FROM cur1 INTO DESCRIPTOR sqlda1; + + + + + Next, retrieve the fetched records from the SQLDA, by following + the linked list of the sqlda_t structure. + + for (cur_sqlda = sqlda1 ; + cur_sqlda != NULL ; + cur_sqlda = cur_sqlda->desc_next) + { + ... + + + + + Read each columns in the first record. The number of columns is + stored in sqld, the actual data of the first + column is stored in sqlvar[0], both members of + the sqlda_t structure. + + + /* Print every column in a row. */ + for (i = 0; i < sqlda1->sqld; i++) + { + sqlvar_t v = sqlda1->sqlvar[i]; + char *sqldata = v.sqldata; + short sqllen = v.sqllen; + + strncpy(name_buf, v.sqlname.data, v.sqlname.length); + name_buf[v.sqlname.length] = '\0'; + + + + + Now, the column data is stored in the variable v. + Copy every datum into host variables, looking + at v.sqltype for the type of the column. + + switch (v.sqltype) { + int intval; + double doubleval; + unsigned long long int longlongval; + + case ECPGt_char: + memset(&var_buf, 0, sizeof(var_buf)); + memcpy(&var_buf, sqldata, (sizeof(var_buf) <= sqllen ? sizeof(var_buf)-1 : sqllen)); + break; + + case ECPGt_int: /* integer */ + memcpy(&intval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%d", intval); + break; + + ... + + default: + ... + } + + printf("%s = %s (type: %d)\n", name_buf, var_buf, v.sqltype); + } + + + + + Close the cursor after processing all of records, and disconnect + from the database. + + EXEC SQL CLOSE cur1; + EXEC SQL COMMIT; + + EXEC SQL DISCONNECT ALL; + + + + + The whole program is shown + in . + + + + Example SQLDA Program + +#include <stdlib.h> +#include <string.h> +#include <stdlib.h> +#include <stdio.h> +#include <unistd.h> + +EXEC SQL include sqlda.h; + +sqlda_t *sqlda1; /* descriptor for output */ +sqlda_t *sqlda2; /* descriptor for input */ + +EXEC SQL WHENEVER NOT FOUND DO BREAK; +EXEC SQL WHENEVER SQLERROR STOP; + +int +main(void) +{ + EXEC SQL BEGIN DECLARE SECTION; + char query[1024] = "SELECT d.oid,* FROM pg_database d, pg_stat_database s WHERE d.oid=s.datid AND ( d.datname=? OR d.oid=? )"; + + int intval; + unsigned long long int longlongval; + EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO uptimedb AS con1 USER uptime; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + EXEC SQL PREPARE stmt1 FROM :query; + EXEC SQL DECLARE cur1 CURSOR FOR stmt1; + + /* Create a SQLDA structure for an input parameter */ + sqlda2 = (sqlda_t *)malloc(sizeof(sqlda_t) + sizeof(sqlvar_t)); + memset(sqlda2, 0, sizeof(sqlda_t) + sizeof(sqlvar_t)); + sqlda2->sqln = 2; /* a number of input variables */ + + sqlda2->sqlvar[0].sqltype = ECPGt_char; + sqlda2->sqlvar[0].sqldata = "postgres"; + sqlda2->sqlvar[0].sqllen = 8; + + intval = 1; + sqlda2->sqlvar[1].sqltype = ECPGt_int; + sqlda2->sqlvar[1].sqldata = (char *) &intval; + sqlda2->sqlvar[1].sqllen = sizeof(intval); + + /* Open a cursor with input parameters. */ + EXEC SQL OPEN cur1 USING DESCRIPTOR sqlda2; + + while (1) + { + sqlda_t *cur_sqlda; + + /* Assign descriptor to the cursor */ + EXEC SQL FETCH NEXT FROM cur1 INTO DESCRIPTOR sqlda1; + + for (cur_sqlda = sqlda1 ; + cur_sqlda != NULL ; + cur_sqlda = cur_sqlda->desc_next) + { + int i; + char name_buf[1024]; + char var_buf[1024]; + + /* Print every column in a row. */ + for (i=0 ; i<cur_sqlda->sqld ; i++) + { + sqlvar_t v = cur_sqlda->sqlvar[i]; + char *sqldata = v.sqldata; + short sqllen = v.sqllen; + + strncpy(name_buf, v.sqlname.data, v.sqlname.length); + name_buf[v.sqlname.length] = '\0'; + + switch (v.sqltype) + { + case ECPGt_char: + memset(&var_buf, 0, sizeof(var_buf)); + memcpy(&var_buf, sqldata, (sizeof(var_buf)<=sqllen ? sizeof(var_buf)-1 : sqllen) ); + break; + + case ECPGt_int: /* integer */ + memcpy(&intval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%d", intval); + break; + + case ECPGt_long_long: /* bigint */ + memcpy(&longlongval, sqldata, sqllen); + snprintf(var_buf, sizeof(var_buf), "%lld", longlongval); + break; + + default: + { + int i; + memset(var_buf, 0, sizeof(var_buf)); + for (i = 0; i < sqllen; i++) + { + char tmpbuf[16]; + snprintf(tmpbuf, sizeof(tmpbuf), "%02x ", (unsigned char) sqldata[i]); + strncat(var_buf, tmpbuf, sizeof(var_buf)); + } + } + break; + } + + printf("%s = %s (type: %d)\n", name_buf, var_buf, v.sqltype); + } + + printf("\n"); + } + } + + EXEC SQL CLOSE cur1; + EXEC SQL COMMIT; + + EXEC SQL DISCONNECT ALL; + + return 0; +} + + + + The output of this example should look something like the + following (some numbers will vary). + + + +oid = 1 (type: 1) +datname = template1 (type: 1) +datdba = 10 (type: 1) +encoding = 0 (type: 5) +datistemplate = t (type: 1) +datallowconn = t (type: 1) +datconnlimit = -1 (type: 5) +datlastsysoid = 11510 (type: 1) +datfrozenxid = 379 (type: 1) +dattablespace = 1663 (type: 1) +datconfig = (type: 1) +datacl = {=c/uptime,uptime=CTc/uptime} (type: 1) +datid = 1 (type: 1) +datname = template1 (type: 1) +numbackends = 0 (type: 5) +xact_commit = 113606 (type: 9) +xact_rollback = 0 (type: 9) +blks_read = 130 (type: 9) +blks_hit = 7341714 (type: 9) +tup_returned = 38262679 (type: 9) +tup_fetched = 1836281 (type: 9) +tup_inserted = 0 (type: 9) +tup_updated = 0 (type: 9) +tup_deleted = 0 (type: 9) + +oid = 11511 (type: 1) +datname = postgres (type: 1) +datdba = 10 (type: 1) +encoding = 0 (type: 5) +datistemplate = f (type: 1) +datallowconn = t (type: 1) +datconnlimit = -1 (type: 5) +datlastsysoid = 11510 (type: 1) +datfrozenxid = 379 (type: 1) +dattablespace = 1663 (type: 1) +datconfig = (type: 1) +datacl = (type: 1) +datid = 11511 (type: 1) +datname = postgres (type: 1) +numbackends = 0 (type: 5) +xact_commit = 221069 (type: 9) +xact_rollback = 18 (type: 9) +blks_read = 1176 (type: 9) +blks_hit = 13943750 (type: 9) +tup_returned = 77410091 (type: 9) +tup_fetched = 3253694 (type: 9) +tup_inserted = 0 (type: 9) +tup_updated = 0 (type: 9) +tup_deleted = 0 (type: 9) + + + + + + + + Error Handling + + + This section describes how you can handle exceptional conditions + and warnings in an embedded SQL program. There are two + nonexclusive facilities for this. + + + + + Callbacks can be configured to handle warning and error + conditions using the WHENEVER command. + + + + + + Detailed information about the error or warning can be obtained + from the sqlca variable. + + + + + + + Setting Callbacks + + + One simple method to catch errors and warnings is to set a + specific action to be executed whenever a particular condition + occurs. In general: + +EXEC SQL WHENEVER condition action; + + + + + condition can be one of the following: + + + + SQLERROR + + + The specified action is called whenever an error occurs during + the execution of an SQL statement. + + + + + + SQLWARNING + + + The specified action is called whenever a warning occurs + during the execution of an SQL statement. + + + + + + NOT FOUND + + + The specified action is called whenever an SQL statement + retrieves or affects zero rows. (This condition is not an + error, but you might be interested in handling it specially.) + + + + + + + + action can be one of the following: + + + + CONTINUE + + + This effectively means that the condition is ignored. This is + the default. + + + + + + GOTO label + GO TO label + + + Jump to the specified label (using a C goto + statement). + + + + + + SQLPRINT + + + Print a message to standard error. This is useful for simple + programs or during prototyping. The details of the message + cannot be configured. + + + + + + STOP + + + Call exit(1), which will terminate the + program. + + + + + + DO BREAK + + + Execute the C statement break. This should + only be used in loops or switch statements. + + + + + + DO CONTINUE + + + Execute the C statement continue. This should + only be used in loops statements. if executed, will cause the flow + of control to return to the top of the loop. + + + + + + CALL name (args) + DO name (args) + + + Call the specified C functions with the specified arguments. (This + use is different from the meaning of CALL + and DO in the normal PostgreSQL grammar.) + + + + + + The SQL standard only provides for the actions + CONTINUE and GOTO (and + GO TO). + + + + Here is an example that you might want to use in a simple program. + It prints a simple message when a warning occurs and aborts the + program when an error happens: + +EXEC SQL WHENEVER SQLWARNING SQLPRINT; +EXEC SQL WHENEVER SQLERROR STOP; + + + + + The statement EXEC SQL WHENEVER is a directive + of the SQL preprocessor, not a C statement. The error or warning + actions that it sets apply to all embedded SQL statements that + appear below the point where the handler is set, unless a + different action was set for the same condition between the first + EXEC SQL WHENEVER and the SQL statement causing + the condition, regardless of the flow of control in the C program. + So neither of the two following C program excerpts will have the + desired effect: + +/* + * WRONG + */ +int main(int argc, char *argv[]) +{ + ... + if (verbose) { + EXEC SQL WHENEVER SQLWARNING SQLPRINT; + } + ... + EXEC SQL SELECT ...; + ... +} + + + +/* + * WRONG + */ +int main(int argc, char *argv[]) +{ + ... + set_error_handler(); + ... + EXEC SQL SELECT ...; + ... +} + +static void set_error_handler(void) +{ + EXEC SQL WHENEVER SQLERROR STOP; +} + + + + + + sqlca + + + For more powerful error handling, the embedded SQL interface + provides a global variable with the name sqlca + (SQL communication area) + that has the following structure: + +struct +{ + char sqlcaid[8]; + long sqlabc; + long sqlcode; + struct + { + int sqlerrml; + char sqlerrmc[SQLERRMC_LEN]; + } sqlerrm; + char sqlerrp[8]; + long sqlerrd[6]; + char sqlwarn[8]; + char sqlstate[5]; +} sqlca; + + (In a multithreaded program, every thread automatically gets its + own copy of sqlca. This works similarly to the + handling of the standard C global variable + errno.) + + + + sqlca covers both warnings and errors. If + multiple warnings or errors occur during the execution of a + statement, then sqlca will only contain + information about the last one. + + + + If no error occurred in the last SQL statement, + sqlca.sqlcode will be 0 and + sqlca.sqlstate will be + "00000". If a warning or error occurred, then + sqlca.sqlcode will be negative and + sqlca.sqlstate will be different from + "00000". A positive + sqlca.sqlcode indicates a harmless condition, + such as that the last query returned zero rows. + sqlcode and sqlstate are two + different error code schemes; details appear below. + + + + If the last SQL statement was successful, then + sqlca.sqlerrd[1] contains the OID of the + processed row, if applicable, and + sqlca.sqlerrd[2] contains the number of + processed or returned rows, if applicable to the command. + + + + In case of an error or warning, + sqlca.sqlerrm.sqlerrmc will contain a string + that describes the error. The field + sqlca.sqlerrm.sqlerrml contains the length of + the error message that is stored in + sqlca.sqlerrm.sqlerrmc (the result of + strlen(), not really interesting for a C + programmer). Note that some messages are too long to fit in the + fixed-size sqlerrmc array; they will be truncated. + + + + In case of a warning, sqlca.sqlwarn[2] is set + to W. (In all other cases, it is set to + something different from W.) If + sqlca.sqlwarn[1] is set to + W, then a value was truncated when it was + stored in a host variable. sqlca.sqlwarn[0] is + set to W if any of the other elements are set + to indicate a warning. + + + + The fields sqlcaid, + sqlabc, + sqlerrp, and the remaining elements of + sqlerrd and + sqlwarn currently contain no useful + information. + + + + The structure sqlca is not defined in the SQL + standard, but is implemented in several other SQL database + systems. The definitions are similar at the core, but if you want + to write portable applications, then you should investigate the + different implementations carefully. + + + + Here is one example that combines the use of WHENEVER + and sqlca, printing out the contents + of sqlca when an error occurs. This is perhaps + useful for debugging or prototyping applications, before + installing a more user-friendly error handler. + + +EXEC SQL WHENEVER SQLERROR CALL print_sqlca(); + +void +print_sqlca() +{ + fprintf(stderr, "==== sqlca ====\n"); + fprintf(stderr, "sqlcode: %ld\n", sqlca.sqlcode); + fprintf(stderr, "sqlerrm.sqlerrml: %d\n", sqlca.sqlerrm.sqlerrml); + fprintf(stderr, "sqlerrm.sqlerrmc: %s\n", sqlca.sqlerrm.sqlerrmc); + fprintf(stderr, "sqlerrd: %ld %ld %ld %ld %ld %ld\n", sqlca.sqlerrd[0],sqlca.sqlerrd[1],sqlca.sqlerrd[2], + sqlca.sqlerrd[3],sqlca.sqlerrd[4],sqlca.sqlerrd[5]); + fprintf(stderr, "sqlwarn: %d %d %d %d %d %d %d %d\n", sqlca.sqlwarn[0], sqlca.sqlwarn[1], sqlca.sqlwarn[2], + sqlca.sqlwarn[3], sqlca.sqlwarn[4], sqlca.sqlwarn[5], + sqlca.sqlwarn[6], sqlca.sqlwarn[7]); + fprintf(stderr, "sqlstate: %5s\n", sqlca.sqlstate); + fprintf(stderr, "===============\n"); +} + + + The result could look as follows (here an error due to a + misspelled table name): + + +==== sqlca ==== +sqlcode: -400 +sqlerrm.sqlerrml: 49 +sqlerrm.sqlerrmc: relation "pg_databasep" does not exist on line 38 +sqlerrd: 0 0 0 0 0 0 +sqlwarn: 0 0 0 0 0 0 0 0 +sqlstate: 42P01 +=============== + + + + + + <literal>SQLSTATE</literal> vs. <literal>SQLCODE</literal> + + + The fields sqlca.sqlstate and + sqlca.sqlcode are two different schemes that + provide error codes. Both are derived from the SQL standard, but + SQLCODE has been marked deprecated in the SQL-92 + edition of the standard and has been dropped in later editions. + Therefore, new applications are strongly encouraged to use + SQLSTATE. + + + + SQLSTATE is a five-character array. The five + characters contain digits or upper-case letters that represent + codes of various error and warning conditions. + SQLSTATE has a hierarchical scheme: the first + two characters indicate the general class of the condition, the + last three characters indicate a subclass of the general + condition. A successful state is indicated by the code + 00000. The SQLSTATE codes are for + the most part defined in the SQL standard. The + PostgreSQL server natively supports + SQLSTATE error codes; therefore a high degree + of consistency can be achieved by using this error code scheme + throughout all applications. For further information see + . + + + + SQLCODE, the deprecated error code scheme, is a + simple integer. A value of 0 indicates success, a positive value + indicates success with additional information, a negative value + indicates an error. The SQL standard only defines the positive + value +100, which indicates that the last command returned or + affected zero rows, and no specific negative values. Therefore, + this scheme can only achieve poor portability and does not have a + hierarchical code assignment. Historically, the embedded SQL + processor for PostgreSQL has assigned + some specific SQLCODE values for its use, which + are listed below with their numeric value and their symbolic name. + Remember that these are not portable to other SQL implementations. + To simplify the porting of applications to the + SQLSTATE scheme, the corresponding + SQLSTATE is also listed. There is, however, no + one-to-one or one-to-many mapping between the two schemes (indeed + it is many-to-many), so you should consult the global + SQLSTATE listing in + in each case. + + + + These are the assigned SQLCODE values: + + + + 0 (ECPG_NO_ERROR) + + + Indicates no error. (SQLSTATE 00000) + + + + + + 100 (ECPG_NOT_FOUND) + + + This is a harmless condition indicating that the last command + retrieved or processed zero rows, or that you are at the end of + the cursor. (SQLSTATE 02000) + + + + When processing a cursor in a loop, you could use this code as + a way to detect when to abort the loop, like this: + +while (1) +{ + EXEC SQL FETCH ... ; + if (sqlca.sqlcode == ECPG_NOT_FOUND) + break; +} + + But WHENEVER NOT FOUND DO BREAK effectively + does this internally, so there is usually no advantage in + writing this out explicitly. + + + + + + -12 (ECPG_OUT_OF_MEMORY) + + + Indicates that your virtual memory is exhausted. The numeric + value is defined as -ENOMEM. (SQLSTATE + YE001) + + + + + + -200 (ECPG_UNSUPPORTED) + + + Indicates the preprocessor has generated something that the + library does not know about. Perhaps you are running + incompatible versions of the preprocessor and the + library. (SQLSTATE YE002) + + + + + + -201 (ECPG_TOO_MANY_ARGUMENTS) + + + This means that the command specified more host variables than + the command expected. (SQLSTATE 07001 or 07002) + + + + + + -202 (ECPG_TOO_FEW_ARGUMENTS) + + + This means that the command specified fewer host variables than + the command expected. (SQLSTATE 07001 or 07002) + + + + + + -203 (ECPG_TOO_MANY_MATCHES) + + + This means a query has returned multiple rows but the statement + was only prepared to store one result row (for example, because + the specified variables are not arrays). (SQLSTATE 21000) + + + + + + -204 (ECPG_INT_FORMAT) + + + The host variable is of type int and the datum in + the database is of a different type and contains a value that + cannot be interpreted as an int. The library uses + strtol() for this conversion. (SQLSTATE + 42804) + + + + + + -205 (ECPG_UINT_FORMAT) + + + The host variable is of type unsigned int and the + datum in the database is of a different type and contains a + value that cannot be interpreted as an unsigned + int. The library uses strtoul() + for this conversion. (SQLSTATE 42804) + + + + + + -206 (ECPG_FLOAT_FORMAT) + + + The host variable is of type float and the datum + in the database is of another type and contains a value that + cannot be interpreted as a float. The library + uses strtod() for this conversion. + (SQLSTATE 42804) + + + + + + -207 (ECPG_NUMERIC_FORMAT) + + + The host variable is of type numeric and the datum + in the database is of another type and contains a value that + cannot be interpreted as a numeric value. + (SQLSTATE 42804) + + + + + + -208 (ECPG_INTERVAL_FORMAT) + + + The host variable is of type interval and the datum + in the database is of another type and contains a value that + cannot be interpreted as an interval value. + (SQLSTATE 42804) + + + + + + -209 (ECPG_DATE_FORMAT) + + + The host variable is of type date and the datum in + the database is of another type and contains a value that + cannot be interpreted as a date value. + (SQLSTATE 42804) + + + + + + -210 (ECPG_TIMESTAMP_FORMAT) + + + The host variable is of type timestamp and the + datum in the database is of another type and contains a value + that cannot be interpreted as a timestamp value. + (SQLSTATE 42804) + + + + + + -211 (ECPG_CONVERT_BOOL) + + + This means the host variable is of type bool and + the datum in the database is neither 't' nor + 'f'. (SQLSTATE 42804) + + + + + + -212 (ECPG_EMPTY) + + + The statement sent to the PostgreSQL + server was empty. (This cannot normally happen in an embedded + SQL program, so it might point to an internal error.) (SQLSTATE + YE002) + + + + + + -213 (ECPG_MISSING_INDICATOR) + + + A null value was returned and no null indicator variable was + supplied. (SQLSTATE 22002) + + + + + + -214 (ECPG_NO_ARRAY) + + + An ordinary variable was used in a place that requires an + array. (SQLSTATE 42804) + + + + + + -215 (ECPG_DATA_NOT_ARRAY) + + + The database returned an ordinary variable in a place that + requires array value. (SQLSTATE 42804) + + + + + + -216 (ECPG_ARRAY_INSERT) + + + The value could not be inserted into the array. (SQLSTATE + 42804) + + + + + + -220 (ECPG_NO_CONN) + + + The program tried to access a connection that does not exist. + (SQLSTATE 08003) + + + + + + -221 (ECPG_NOT_CONN) + + + The program tried to access a connection that does exist but is + not open. (This is an internal error.) (SQLSTATE YE002) + + + + + + -230 (ECPG_INVALID_STMT) + + + The statement you are trying to use has not been prepared. + (SQLSTATE 26000) + + + + + + -239 (ECPG_INFORMIX_DUPLICATE_KEY) + + + Duplicate key error, violation of unique constraint (Informix + compatibility mode). (SQLSTATE 23505) + + + + + + -240 (ECPG_UNKNOWN_DESCRIPTOR) + + + The descriptor specified was not found. The statement you are + trying to use has not been prepared. (SQLSTATE 33000) + + + + + + -241 (ECPG_INVALID_DESCRIPTOR_INDEX) + + + The descriptor index specified was out of range. (SQLSTATE + 07009) + + + + + + -242 (ECPG_UNKNOWN_DESCRIPTOR_ITEM) + + + An invalid descriptor item was requested. (This is an internal + error.) (SQLSTATE YE002) + + + + + + -243 (ECPG_VAR_NOT_NUMERIC) + + + During the execution of a dynamic statement, the database + returned a numeric value and the host variable was not numeric. + (SQLSTATE 07006) + + + + + + -244 (ECPG_VAR_NOT_CHAR) + + + During the execution of a dynamic statement, the database + returned a non-numeric value and the host variable was numeric. + (SQLSTATE 07006) + + + + + + -284 (ECPG_INFORMIX_SUBSELECT_NOT_ONE) + + + A result of the subquery is not single row (Informix + compatibility mode). (SQLSTATE 21000) + + + + + + -400 (ECPG_PGSQL) + + + Some error caused by the PostgreSQL + server. The message contains the error message from the + PostgreSQL server. + + + + + + -401 (ECPG_TRANS) + + + The PostgreSQL server signaled that + we cannot start, commit, or rollback the transaction. + (SQLSTATE 08007) + + + + + + -402 (ECPG_CONNECT) + + + The connection attempt to the database did not succeed. + (SQLSTATE 08001) + + + + + + -403 (ECPG_DUPLICATE_KEY) + + + Duplicate key error, violation of unique constraint. (SQLSTATE + 23505) + + + + + + -404 (ECPG_SUBSELECT_NOT_ONE) + + + A result for the subquery is not single row. (SQLSTATE 21000) + + + + + + + + + -602 (ECPG_WARNING_UNKNOWN_PORTAL) + + + An invalid cursor name was specified. (SQLSTATE 34000) + + + + + + -603 (ECPG_WARNING_IN_TRANSACTION) + + + Transaction is in progress. (SQLSTATE 25001) + + + + + + -604 (ECPG_WARNING_NO_TRANSACTION) + + + There is no active (in-progress) transaction. (SQLSTATE 25P01) + + + + + + -605 (ECPG_WARNING_PORTAL_EXISTS) + + + An existing cursor name was specified. (SQLSTATE 42P03) + + + + + + + + + + + Preprocessor Directives + + + Several preprocessor directives are available that modify how + the ecpg preprocessor parses and processes a + file. + + + + Including Files + + + To include an external file into your embedded SQL program, use: + +EXEC SQL INCLUDE filename; +EXEC SQL INCLUDE <filename>; +EXEC SQL INCLUDE "filename"; + + The embedded SQL preprocessor will look for a file named + filename.h, + preprocess it, and include it in the resulting C output. Thus, + embedded SQL statements in the included file are handled correctly. + + + + The ecpg preprocessor will search a file at + several directories in following order: + + + current directory + /usr/local/include + PostgreSQL include directory, defined at build time (e.g., /usr/local/pgsql/include) + /usr/include + + + But when EXEC SQL INCLUDE + "filename" is used, only the + current directory is searched. + + + + In each directory, the preprocessor will first look for the file + name as given, and if not found will append .h + to the file name and try again (unless the specified file name + already has that suffix). + + + + Note that EXEC SQL INCLUDE is not the same as: + +#include <filename.h> + + because this file would not be subject to SQL command preprocessing. + Naturally, you can continue to use the C + #include directive to include other header + files. + + + + + The include file name is case-sensitive, even though the rest of + the EXEC SQL INCLUDE command follows the normal + SQL case-sensitivity rules. + + + + + + The define and undef Directives + + Similar to the directive #define that is known from C, + embedded SQL has a similar concept: + +EXEC SQL DEFINE name; +EXEC SQL DEFINE name value; + + So you can define a name: + +EXEC SQL DEFINE HAVE_FEATURE; + + And you can also define constants: + +EXEC SQL DEFINE MYNUMBER 12; +EXEC SQL DEFINE MYSTRING 'abc'; + + Use undef to remove a previous definition: + +EXEC SQL UNDEF MYNUMBER; + + + + + Of course you can continue to use the C versions #define + and #undef in your embedded SQL program. The difference + is where your defined values get evaluated. If you use EXEC SQL + DEFINE then the ecpg preprocessor evaluates the defines and substitutes + the values. For example if you write: + +EXEC SQL DEFINE MYNUMBER 12; +... +EXEC SQL UPDATE Tbl SET col = MYNUMBER; + + then ecpg will already do the substitution and your C compiler will never + see any name or identifier MYNUMBER. Note that you cannot use + #define for a constant that you are going to use in an + embedded SQL query because in this case the embedded SQL precompiler is not + able to see this declaration. + + + + + ifdef, ifndef, elif, else, and endif Directives + + You can use the following directives to compile code sections conditionally: + + + + EXEC SQL ifdef name; + + + Checks a name and processes subsequent lines if + name has been defined via EXEC SQL define + name. + + + + + + EXEC SQL ifndef name; + + + Checks a name and processes subsequent lines if + name has not been defined via + EXEC SQL define name. + + + + + + EXEC SQL elif name; + + + Begins an optional alternative section after an + EXEC SQL ifdef name or + EXEC SQL ifndef name + directive. Any number of elif sections can appear. + Lines following an elif will be processed + if name has been + defined and no previous section of the same + ifdef/ifndef...endif + construct has been processed. + + + + + + EXEC SQL else; + + + Begins an optional, final alternative section after an + EXEC SQL ifdef name or + EXEC SQL ifndef name + directive. Subsequent lines will be processed if no previous section + of the same + ifdef/ifndef...endif + construct has been processed. + + + + + + EXEC SQL endif; + + + Ends an + ifdef/ifndef...endif + construct. Subsequent lines are processed normally. + + + + + + + + ifdef/ifndef...endif + constructs can be nested, up to 127 levels deep. + + + + This example will compile exactly one of the three SET + TIMEZONE commands: + +EXEC SQL ifdef TZVAR; +EXEC SQL SET TIMEZONE TO TZVAR; +EXEC SQL elif TZNAME; +EXEC SQL SET TIMEZONE TO TZNAME; +EXEC SQL else; +EXEC SQL SET TIMEZONE TO 'GMT'; +EXEC SQL endif; + + + + + + + + Processing Embedded SQL Programs + + + Now that you have an idea how to form embedded SQL C programs, you + probably want to know how to compile them. Before compiling you + run the file through the embedded SQL + C preprocessor, which converts the + SQL statements you used to special function + calls. After compiling, you must link with a special library that + contains the needed functions. These functions fetch information + from the arguments, perform the SQL command using + the libpq interface, and put the result + in the arguments specified for output. + + + + The preprocessor program is called ecpg and is + included in a normal PostgreSQL installation. + Embedded SQL programs are typically named with an extension + .pgc. If you have a program file called + prog1.pgc, you can preprocess it by simply + calling: + +ecpg prog1.pgc + + This will create a file called prog1.c. If + your input files do not follow the suggested naming pattern, you + can specify the output file explicitly using the + option. + + + + The preprocessed file can be compiled normally, for example: + +cc -c prog1.c + + The generated C source files include header files from the + PostgreSQL installation, so if you installed + PostgreSQL in a location that is not searched by + default, you have to add an option such as + -I/usr/local/pgsql/include to the compilation + command line. + + + + To link an embedded SQL program, you need to include the + libecpg library, like so: + +cc -o myprog prog1.o prog2.o ... -lecpg + + Again, you might have to add an option like + -L/usr/local/pgsql/lib to that command line. + + + + You can + use pg_configpg_configwith + ecpg + or pkg-configpkg-configwith + ecpg with package name libecpg to + get the paths for your installation. + + + + If you manage the build process of a larger project using + make, it might be convenient to include + the following implicit rule to your makefiles: + +ECPG = ecpg + +%.c: %.pgc + $(ECPG) $< + + + + + The complete syntax of the ecpg command is + detailed in . + + + + The ecpg library is thread-safe by + default. However, you might need to use some threading + command-line options to compile your client code. + + + + + Library Functions + + + The libecpg library primarily contains + hidden functions that are used to implement the + functionality expressed by the embedded SQL commands. But there + are some functions that can usefully be called directly. Note that + this makes your code unportable. + + + + + + ECPGdebug(int on, FILE + *stream) turns on debug + logging if called with the first argument non-zero. Debug logging + is done on stream. The log contains + all SQL statements with all the input + variables inserted, and the results from the + PostgreSQL server. This can be very + useful when searching for errors in your SQL + statements. + + + + On Windows, if the ecpg libraries and an application are + compiled with different flags, this function call will crash the + application because the internal representation of the + FILE pointers differ. Specifically, + multithreaded/single-threaded, release/debug, and static/dynamic + flags should be the same for the library and all applications using + that library. + + + + + + + ECPGget_PGconn(const char *connection_name) + returns the library database connection handle identified by the given name. + If connection_name is set to NULL, the current + connection handle is returned. If no connection handle can be identified, the function returns + NULL. The returned connection handle can be used to call any other functions + from libpq, if necessary. + + + + It is a bad idea to manipulate database connection handles made from ecpg directly + with libpq routines. + + + + + + + ECPGtransactionStatus(const char *connection_name) + returns the current transaction status of the given connection identified by connection_name. + See and libpq's for details about the returned status codes. + + + + + + ECPGstatus(int lineno, + const char* connection_name) + returns true if you are connected to a database and false if not. + connection_name can be NULL + if a single connection is being used. + + + + + + + Large Objects + + + Large objects are not directly supported by ECPG, but ECPG + application can manipulate large objects through the libpq large + object functions, obtaining the necessary PGconn + object by calling the ECPGget_PGconn() + function. (However, use of + the ECPGget_PGconn() function and touching + PGconn objects directly should be done very carefully + and ideally not mixed with other ECPG database access calls.) + + + + For more details about the ECPGget_PGconn(), see + . For information about the large + object function interface, see . + + + + Large object functions have to be called in a transaction block, so + when autocommit is off, BEGIN commands have to + be issued explicitly. + + + + shows an example program that + illustrates how to create, write, and read a large object in an + ECPG application. + + + + ECPG Program Accessing Large Objects + +#include +#include +#include + +EXEC SQL WHENEVER SQLERROR STOP; + +int +main(void) +{ + PGconn *conn; + Oid loid; + int fd; + char buf[256]; + int buflen = 256; + char buf2[256]; + int rc; + + memset(buf, 1, buflen); + + EXEC SQL CONNECT TO testdb AS con1; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + conn = ECPGget_PGconn("con1"); + printf("conn = %p\n", conn); + + /* create */ + loid = lo_create(conn, 0); + if (loid < 0) + printf("lo_create() failed: %s", PQerrorMessage(conn)); + + printf("loid = %d\n", loid); + + /* write test */ + fd = lo_open(conn, loid, INV_READ|INV_WRITE); + if (fd < 0) + printf("lo_open() failed: %s", PQerrorMessage(conn)); + + printf("fd = %d\n", fd); + + rc = lo_write(conn, fd, buf, buflen); + if (rc < 0) + printf("lo_write() failed\n"); + + rc = lo_close(conn, fd); + if (rc < 0) + printf("lo_close() failed: %s", PQerrorMessage(conn)); + + /* read test */ + fd = lo_open(conn, loid, INV_READ); + if (fd < 0) + printf("lo_open() failed: %s", PQerrorMessage(conn)); + + printf("fd = %d\n", fd); + + rc = lo_read(conn, fd, buf2, buflen); + if (rc < 0) + printf("lo_read() failed\n"); + + rc = lo_close(conn, fd); + if (rc < 0) + printf("lo_close() failed: %s", PQerrorMessage(conn)); + + /* check */ + rc = memcmp(buf, buf2, buflen); + printf("memcmp() = %d\n", rc); + + /* cleanup */ + rc = lo_unlink(conn, loid); + if (rc < 0) + printf("lo_unlink() failed: %s", PQerrorMessage(conn)); + + EXEC SQL COMMIT; + EXEC SQL DISCONNECT ALL; + return 0; +} +]]> + + + + + <acronym>C++</acronym> Applications + + + ECPG has some limited support for C++ applications. This section + describes some caveats. + + + + The ecpg preprocessor takes an input file + written in C (or something like C) and embedded SQL commands, + converts the embedded SQL commands into C language chunks, and + finally generates a .c file. The header file + declarations of the library functions used by the C language chunks + that ecpg generates are wrapped + in extern "C" { ... } blocks when used under + C++, so they should work seamlessly in C++. + + + + In general, however, the ecpg preprocessor only + understands C; it does not handle the special syntax and reserved + words of the C++ language. So, some embedded SQL code written in + C++ application code that uses complicated features specific to C++ + might fail to be preprocessed correctly or might not work as + expected. + + + + A safe way to use the embedded SQL code in a C++ application is + hiding the ECPG calls in a C module, which the C++ application code + calls into to access the database, and linking that together with + the rest of the C++ code. See + about that. + + + + Scope for Host Variables + + + The ecpg preprocessor understands the scope of + variables in C. In the C language, this is rather simple because + the scopes of variables is based on their code blocks. In C++, + however, the class member variables are referenced in a different + code block from the declared position, so + the ecpg preprocessor will not understand the + scope of the class member variables. + + + + For example, in the following case, the ecpg + preprocessor cannot find any declaration for the + variable dbname in the test + method, so an error will occur. + + +class TestCpp +{ + EXEC SQL BEGIN DECLARE SECTION; + char dbname[1024]; + EXEC SQL END DECLARE SECTION; + + public: + TestCpp(); + void test(); + ~TestCpp(); +}; + +TestCpp::TestCpp() +{ + EXEC SQL CONNECT TO testdb1; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; +} + +void Test::test() +{ + EXEC SQL SELECT current_database() INTO :dbname; + printf("current_database = %s\n", dbname); +} + +TestCpp::~TestCpp() +{ + EXEC SQL DISCONNECT ALL; +} + + + This code will result in an error like this: + +ecpg test_cpp.pgc +test_cpp.pgc:28: ERROR: variable "dbname" is not declared + + + + + To avoid this scope issue, the test method + could be modified to use a local variable as intermediate storage. + But this approach is only a poor workaround, because it uglifies + the code and reduces performance. + + +void TestCpp::test() +{ + EXEC SQL BEGIN DECLARE SECTION; + char tmp[1024]; + EXEC SQL END DECLARE SECTION; + + EXEC SQL SELECT current_database() INTO :tmp; + strlcpy(dbname, tmp, sizeof(tmp)); + + printf("current_database = %s\n", dbname); +} + + + + + + C++ Application Development with External C Module + + + If you understand these technical limitations of + the ecpg preprocessor in C++, you might come to + the conclusion that linking C objects and C++ objects at the link + stage to enable C++ applications to use ECPG features could be + better than writing some embedded SQL commands in C++ code + directly. This section describes a way to separate some embedded + SQL commands from C++ application code with a simple example. In + this example, the application is implemented in C++, while C and + ECPG is used to connect to the PostgreSQL server. + + + + Three kinds of files have to be created: a C file + (*.pgc), a header file, and a C++ file: + + + + test_mod.pgc + + + A sub-routine module to execute SQL commands embedded in C. + It is going to be converted + into test_mod.c by the preprocessor. + + +#include "test_mod.h" +#include <stdio.h> + +void +db_connect() +{ + EXEC SQL CONNECT TO testdb1; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; +} + +void +db_test() +{ + EXEC SQL BEGIN DECLARE SECTION; + char dbname[1024]; + EXEC SQL END DECLARE SECTION; + + EXEC SQL SELECT current_database() INTO :dbname; + printf("current_database = %s\n", dbname); +} + +void +db_disconnect() +{ + EXEC SQL DISCONNECT ALL; +} + + + + + + + test_mod.h + + + A header file with declarations of the functions in the C + module (test_mod.pgc). It is included by + test_cpp.cpp. This file has to have an + extern "C" block around the declarations, + because it will be linked from the C++ module. + + +#ifdef __cplusplus +extern "C" { +#endif + +void db_connect(); +void db_test(); +void db_disconnect(); + +#ifdef __cplusplus +} +#endif + + + + + + + test_cpp.cpp + + + The main code for the application, including + the main routine, and in this example a + C++ class. + + +#include "test_mod.h" + +class TestCpp +{ + public: + TestCpp(); + void test(); + ~TestCpp(); +}; + +TestCpp::TestCpp() +{ + db_connect(); +} + +void +TestCpp::test() +{ + db_test(); +} + +TestCpp::~TestCpp() +{ + db_disconnect(); +} + +int +main(void) +{ + TestCpp *t = new TestCpp(); + + t->test(); + return 0; +} + + + + + + + + + To build the application, proceed as follows. Convert + test_mod.pgc into test_mod.c by + running ecpg, and generate + test_mod.o by compiling + test_mod.c with the C compiler: + +ecpg -o test_mod.c test_mod.pgc +cc -c test_mod.c -o test_mod.o + + + + + Next, generate test_cpp.o by compiling + test_cpp.cpp with the C++ compiler: + +c++ -c test_cpp.cpp -o test_cpp.o + + + + + Finally, link these object files, test_cpp.o + and test_mod.o, into one executable, using the C++ + compiler driver: + +c++ test_cpp.o test_mod.o -lecpg -o test_cpp + + + + + + + Embedded SQL Commands + + + This section describes all SQL commands that are specific to + embedded SQL. Also refer to the SQL commands listed + in , which can also be used in + embedded SQL, unless stated otherwise. + + + + + ALLOCATE DESCRIPTOR + allocate an SQL descriptor area + + + + +ALLOCATE DESCRIPTOR name + + + + + Description + + + ALLOCATE DESCRIPTOR allocates a new named SQL + descriptor area, which can be used to exchange data between the + PostgreSQL server and the host program. + + + + Descriptor areas should be freed after use using + the DEALLOCATE DESCRIPTOR command. + + + + + Parameters + + + + name + + + A name of SQL descriptor, case sensitive. This can be an SQL + identifier or a host variable. + + + + + + + + Examples + + +EXEC SQL ALLOCATE DESCRIPTOR mydesc; + + + + + Compatibility + + + ALLOCATE DESCRIPTOR is specified in the SQL + standard. + + + + + See Also + + + + + + + + + + + + CONNECT + establish a database connection + + + + +CONNECT TO connection_target [ AS connection_name ] [ USER connection_user ] +CONNECT TO DEFAULT +CONNECT connection_user +DATABASE connection_target + + + + + Description + + + The CONNECT command establishes a connection + between the client and the PostgreSQL server. + + + + + Parameters + + + + connection_target + + + connection_target + specifies the target server of the connection on one of + several forms. + + + + [ database_name ] [ @host ] [ :port ] + + + Connect over TCP/IP + + + + + + unix:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ] + + + Connect over Unix-domain sockets + + + + + + tcp:postgresql://host [ :port ] / [ database_name ] [ ?connection_option ] + + + Connect over TCP/IP + + + + + + SQL string constant + + + containing a value in one of the above forms + + + + + + host variable + + + host variable of type char[] + or VARCHAR[] containing a value in one of the + above forms + + + + + + + + + + connection_name + + + An optional identifier for the connection, so that it can be + referred to in other commands. This can be an SQL identifier + or a host variable. + + + + + + connection_user + + + The user name for the database connection. + + + + This parameter can also specify user name and password, using one the forms + user_name/password, + user_name IDENTIFIED BY password, or + user_name USING password. + + + + User name and password can be SQL identifiers, string + constants, or host variables. + + + + + + DEFAULT + + + Use all default connection parameters, as defined by libpq. + + + + + + + + Examples + + + Here a several variants for specifying connection parameters: + +EXEC SQL CONNECT TO "connectdb" AS main; +EXEC SQL CONNECT TO "connectdb" AS second; +EXEC SQL CONNECT TO "unix:postgresql://200.46.204.71/connectdb" AS main USER connectuser; +EXEC SQL CONNECT TO "unix:postgresql://localhost/connectdb" AS main USER connectuser; +EXEC SQL CONNECT TO 'connectdb' AS main; +EXEC SQL CONNECT TO 'unix:postgresql://localhost/connectdb' AS main USER :user; +EXEC SQL CONNECT TO :db AS :id; +EXEC SQL CONNECT TO :db USER connectuser USING :pw; +EXEC SQL CONNECT TO @localhost AS main USER connectdb; +EXEC SQL CONNECT TO REGRESSDB1 as main; +EXEC SQL CONNECT TO AS main USER connectdb; +EXEC SQL CONNECT TO connectdb AS :id; +EXEC SQL CONNECT TO connectdb AS main USER connectuser/connectdb; +EXEC SQL CONNECT TO connectdb AS main; +EXEC SQL CONNECT TO connectdb@localhost AS main; +EXEC SQL CONNECT TO tcp:postgresql://localhost/ USER connectdb; +EXEC SQL CONNECT TO tcp:postgresql://localhost/connectdb USER connectuser IDENTIFIED BY connectpw; +EXEC SQL CONNECT TO tcp:postgresql://localhost:20/connectdb USER connectuser IDENTIFIED BY connectpw; +EXEC SQL CONNECT TO unix:postgresql://localhost/ AS main USER connectdb; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb AS main USER connectuser; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb USER connectuser IDENTIFIED BY "connectpw"; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb USER connectuser USING "connectpw"; +EXEC SQL CONNECT TO unix:postgresql://localhost/connectdb?connect_timeout=14 USER connectuser; + + + + + Here is an example program that illustrates the use of host + variables to specify connection parameters: + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + char *dbname = "testdb"; /* database name */ + char *user = "testuser"; /* connection user name */ + char *connection = "tcp:postgresql://localhost:5432/testdb"; + /* connection string */ + char ver[256]; /* buffer to store the version string */ +EXEC SQL END DECLARE SECTION; + + ECPGdebug(1, stderr); + + EXEC SQL CONNECT TO :dbname USER :user; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + EXEC SQL SELECT version() INTO :ver; + EXEC SQL DISCONNECT; + + printf("version: %s\n", ver); + + EXEC SQL CONNECT TO :connection USER :user; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + EXEC SQL SELECT version() INTO :ver; + EXEC SQL DISCONNECT; + + printf("version: %s\n", ver); + + return 0; +} + + + + + + Compatibility + + + CONNECT is specified in the SQL standard, but + the format of the connection parameters is + implementation-specific. + + + + + See Also + + + + + + + + + + + DEALLOCATE DESCRIPTOR + deallocate an SQL descriptor area + + + + +DEALLOCATE DESCRIPTOR name + + + + + Description + + + DEALLOCATE DESCRIPTOR deallocates a named SQL + descriptor area. + + + + + Parameters + + + + name + + + The name of the descriptor which is going to be deallocated. + It is case sensitive. This can be an SQL identifier or a host + variable. + + + + + + + + Examples + + +EXEC SQL DEALLOCATE DESCRIPTOR mydesc; + + + + + Compatibility + + + DEALLOCATE DESCRIPTOR is specified in the SQL + standard. + + + + + See Also + + + + + + + + + + + + DECLARE + define a cursor + + + + +DECLARE cursor_name [ BINARY ] [ INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ] FOR prepared_name +DECLARE cursor_name [ BINARY ] [ INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ] FOR query + + + + + Description + + + DECLARE declares a cursor for iterating over + the result set of a prepared statement. This command has + slightly different semantics from the direct SQL + command DECLARE: Whereas the latter executes a + query and prepares the result set for retrieval, this embedded + SQL command merely declares a name as a loop + variable for iterating over the result set of a query; + the actual execution happens when the cursor is opened with + the OPEN command. + + + + + Parameters + + + + cursor_name + + + A cursor name, case sensitive. This can be an SQL identifier + or a host variable. + + + + + + prepared_name + + + The name of a prepared query, either as an SQL identifier or a + host variable. + + + + + + query + + + A or + command which will provide the + rows to be returned by the cursor. + + + + + + + For the meaning of the cursor options, + see . + + + + + Examples + + + Examples declaring a cursor for a query: + +EXEC SQL DECLARE C CURSOR FOR SELECT * FROM My_Table; +EXEC SQL DECLARE C CURSOR FOR SELECT Item1 FROM T; +EXEC SQL DECLARE cur1 CURSOR FOR SELECT version(); + + + + + An example declaring a cursor for a prepared statement: + +EXEC SQL PREPARE stmt1 AS SELECT version(); +EXEC SQL DECLARE cur1 CURSOR FOR stmt1; + + + + + + Compatibility + + + DECLARE is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + + DESCRIBE + obtain information about a prepared statement or result set + + + + +DESCRIBE [ OUTPUT ] prepared_name USING [ SQL ] DESCRIPTOR descriptor_name +DESCRIBE [ OUTPUT ] prepared_name INTO [ SQL ] DESCRIPTOR descriptor_name +DESCRIBE [ OUTPUT ] prepared_name INTO sqlda_name + + + + + Description + + + DESCRIBE retrieves metadata information about + the result columns contained in a prepared statement, without + actually fetching a row. + + + + + Parameters + + + + prepared_name + + + The name of a prepared statement. This can be an SQL + identifier or a host variable. + + + + + + descriptor_name + + + A descriptor name. It is case sensitive. It can be an SQL + identifier or a host variable. + + + + + + sqlda_name + + + The name of an SQLDA variable. + + + + + + + + Examples + + +EXEC SQL ALLOCATE DESCRIPTOR mydesc; +EXEC SQL PREPARE stmt1 FROM :sql_stmt; +EXEC SQL DESCRIBE stmt1 INTO SQL DESCRIPTOR mydesc; +EXEC SQL GET DESCRIPTOR mydesc VALUE 1 :charvar = NAME; +EXEC SQL DEALLOCATE DESCRIPTOR mydesc; + + + + + Compatibility + + + DESCRIBE is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + DISCONNECT + terminate a database connection + + + + +DISCONNECT connection_name +DISCONNECT [ CURRENT ] +DISCONNECT DEFAULT +DISCONNECT ALL + + + + + Description + + + DISCONNECT closes a connection (or all + connections) to the database. + + + + + Parameters + + + + connection_name + + + A database connection name established by + the CONNECT command. + + + + + + CURRENT + + + Close the current connection, which is either + the most recently opened connection, or the connection set by + the SET CONNECTION command. This is also + the default if no argument is given to + the DISCONNECT command. + + + + + + DEFAULT + + + Close the default connection. + + + + + + ALL + + + Close all open connections. + + + + + + + + Examples + + +int +main(void) +{ + EXEC SQL CONNECT TO testdb AS DEFAULT USER testuser; + EXEC SQL CONNECT TO testdb AS con1 USER testuser; + EXEC SQL CONNECT TO testdb AS con2 USER testuser; + EXEC SQL CONNECT TO testdb AS con3 USER testuser; + + EXEC SQL DISCONNECT CURRENT; /* close con3 */ + EXEC SQL DISCONNECT DEFAULT; /* close DEFAULT */ + EXEC SQL DISCONNECT ALL; /* close con2 and con1 */ + + return 0; +} + + + + + Compatibility + + + DISCONNECT is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + EXECUTE IMMEDIATE + dynamically prepare and execute a statement + + + + +EXECUTE IMMEDIATE string + + + + + Description + + + EXECUTE IMMEDIATE immediately prepares and + executes a dynamically specified SQL statement, without + retrieving result rows. + + + + + Parameters + + + + string + + + A literal C string or a host variable containing the SQL + statement to be executed. + + + + + + + + Examples + + + Here is an example that executes an INSERT + statement using EXECUTE IMMEDIATE and a host + variable named command: + +sprintf(command, "INSERT INTO test (name, amount, letter) VALUES ('db: ''r1''', 1, 'f')"); +EXEC SQL EXECUTE IMMEDIATE :command; + + + + + + Compatibility + + + EXECUTE IMMEDIATE is specified in the SQL standard. + + + + + + + GET DESCRIPTOR + get information from an SQL descriptor area + + + + +GET DESCRIPTOR descriptor_name :cvariable = descriptor_header_item [, ... ] +GET DESCRIPTOR descriptor_name VALUE column_number :cvariable = descriptor_item [, ... ] + + + + + Description + + + GET DESCRIPTOR retrieves information about a + query result set from an SQL descriptor area and stores it into + host variables. A descriptor area is typically populated + using FETCH or SELECT + before using this command to transfer the information into host + language variables. + + + + This command has two forms: The first form retrieves + descriptor header items, which apply to the result + set in its entirety. One example is the row count. The second + form, which requires the column number as additional parameter, + retrieves information about a particular column. Examples are + the column name and the actual column value. + + + + + Parameters + + + + descriptor_name + + + A descriptor name. + + + + + + descriptor_header_item + + + A token identifying which header information item to retrieve. + Only COUNT, to get the number of columns in the + result set, is currently supported. + + + + + + column_number + + + The number of the column about which information is to be + retrieved. The count starts at 1. + + + + + + descriptor_item + + + A token identifying which item of information about a column + to retrieve. See for + a list of supported items. + + + + + + cvariable + + + A host variable that will receive the data retrieved from the + descriptor area. + + + + + + + + Examples + + + An example to retrieve the number of columns in a result set: + +EXEC SQL GET DESCRIPTOR d :d_count = COUNT; + + + + + An example to retrieve a data length in the first column: + +EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH; + + + + + An example to retrieve the data body of the second column as a + string: + +EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA; + + + + + Here is an example for a whole procedure of + executing SELECT current_database(); and showing the number of + columns, the column data length, and the column data: + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + int d_count; + char d_data[1024]; + int d_returned_octet_length; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb AS con1 USER testuser; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + EXEC SQL ALLOCATE DESCRIPTOR d; + + /* Declare, open a cursor, and assign a descriptor to the cursor */ + EXEC SQL DECLARE cur CURSOR FOR SELECT current_database(); + EXEC SQL OPEN cur; + EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d; + + /* Get a number of total columns */ + EXEC SQL GET DESCRIPTOR d :d_count = COUNT; + printf("d_count = %d\n", d_count); + + /* Get length of a returned column */ + EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH; + printf("d_returned_octet_length = %d\n", d_returned_octet_length); + + /* Fetch the returned column as a string */ + EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA; + printf("d_data = %s\n", d_data); + + /* Closing */ + EXEC SQL CLOSE cur; + EXEC SQL COMMIT; + + EXEC SQL DEALLOCATE DESCRIPTOR d; + EXEC SQL DISCONNECT ALL; + + return 0; +} + + When the example is executed, the result will look like this: + +d_count = 1 +d_returned_octet_length = 6 +d_data = testdb + + + + + + Compatibility + + + GET DESCRIPTOR is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + OPEN + open a dynamic cursor + + + + +OPEN cursor_name +OPEN cursor_name USING value [, ... ] +OPEN cursor_name USING SQL DESCRIPTOR descriptor_name + + + + + Description + + + OPEN opens a cursor and optionally binds + actual values to the placeholders in the cursor's declaration. + The cursor must previously have been declared with + the DECLARE command. The execution + of OPEN causes the query to start executing on + the server. + + + + + Parameters + + + + cursor_name + + + The name of the cursor to be opened. This can be an SQL + identifier or a host variable. + + + + + + value + + + A value to be bound to a placeholder in the cursor. This can + be an SQL constant, a host variable, or a host variable with + indicator. + + + + + + descriptor_name + + + The name of a descriptor containing values to be bound to the + placeholders in the cursor. This can be an SQL identifier or + a host variable. + + + + + + + + Examples + + +EXEC SQL OPEN a; +EXEC SQL OPEN d USING 1, 'test'; +EXEC SQL OPEN c1 USING SQL DESCRIPTOR mydesc; +EXEC SQL OPEN :curname1; + + + + + Compatibility + + + OPEN is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + PREPARE + prepare a statement for execution + + + + +PREPARE name FROM string + + + + + Description + + + PREPARE prepares a statement dynamically + specified as a string for execution. This is different from the + direct SQL statement , which can also + be used in embedded programs. The + command is used to execute either kind of prepared statement. + + + + + Parameters + + + + prepared_name + + + An identifier for the prepared query. + + + + + + string + + + A literal C string or a host variable containing a preparable + statement, one of the SELECT, INSERT, UPDATE, or + DELETE. + + + + + + + + Examples + +char *stmt = "SELECT * FROM test1 WHERE a = ? AND b = ?"; + +EXEC SQL ALLOCATE DESCRIPTOR outdesc; +EXEC SQL PREPARE foo FROM :stmt; + +EXEC SQL EXECUTE foo USING SQL DESCRIPTOR indesc INTO SQL DESCRIPTOR outdesc; + + + + + Compatibility + + + PREPARE is specified in the SQL standard. + + + + + See Also + + + + + + + + + + SET AUTOCOMMIT + set the autocommit behavior of the current session + + + + +SET AUTOCOMMIT { = | TO } { ON | OFF } + + + + + Description + + + SET AUTOCOMMIT sets the autocommit behavior of + the current database session. By default, embedded SQL programs + are not in autocommit mode, + so COMMIT needs to be issued explicitly when + desired. This command can change the session to autocommit mode, + where each individual statement is committed implicitly. + + + + + Compatibility + + + SET AUTOCOMMIT is an extension of PostgreSQL ECPG. + + + + + + + SET CONNECTION + select a database connection + + + + +SET CONNECTION [ TO | = ] connection_name + + + + + Description + + + SET CONNECTION sets the current + database connection, which is the one that all commands use + unless overridden. + + + + + Parameters + + + + connection_name + + + A database connection name established by + the CONNECT command. + + + + + + DEFAULT + + + Set the connection to the default connection. + + + + + + + + Examples + + +EXEC SQL SET CONNECTION TO con2; +EXEC SQL SET CONNECTION = con1; + + + + + Compatibility + + + SET CONNECTION is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + SET DESCRIPTOR + set information in an SQL descriptor area + + + + +SET DESCRIPTOR descriptor_name descriptor_header_item = value [, ... ] +SET DESCRIPTOR descriptor_name VALUE number descriptor_item = value [, ...] + + + + + Description + + + SET DESCRIPTOR populates an SQL descriptor + area with values. The descriptor area is then typically used to + bind parameters in a prepared query execution. + + + + This command has two forms: The first form applies to the + descriptor header, which is independent of a + particular datum. The second form assigns values to particular + datums, identified by number. + + + + + Parameters + + + + descriptor_name + + + A descriptor name. + + + + + + descriptor_header_item + + + A token identifying which header information item to set. + Only COUNT, to set the number of descriptor + items, is currently supported. + + + + + + number + + + The number of the descriptor item to set. The count starts at + 1. + + + + + + descriptor_item + + + A token identifying which item of information to set in the + descriptor. See for a + list of supported items. + + + + + + value + + + A value to store into the descriptor item. This can be an SQL + constant or a host variable. + + + + + + + + Examples + +EXEC SQL SET DESCRIPTOR indesc COUNT = 1; +EXEC SQL SET DESCRIPTOR indesc VALUE 1 DATA = 2; +EXEC SQL SET DESCRIPTOR indesc VALUE 1 DATA = :val1; +EXEC SQL SET DESCRIPTOR indesc VALUE 2 INDICATOR = :val1, DATA = 'some string'; +EXEC SQL SET DESCRIPTOR indesc VALUE 2 INDICATOR = :val2null, DATA = :val2; + + + + + Compatibility + + + SET DESCRIPTOR is specified in the SQL standard. + + + + + See Also + + + + + + + + + + + TYPE + define a new data type + + + + +TYPE type_name IS ctype + + + + + Description + + + The TYPE command defines a new C type. It is + equivalent to putting a typedef into a declare + section. + + + + This command is only recognized when ecpg is + run with the option. + + + + + Parameters + + + + type_name + + + The name for the new type. It must be a valid C type name. + + + + + + ctype + + + A C type specification. + + + + + + + + Examples + + +EXEC SQL TYPE customer IS + struct + { + varchar name[50]; + int phone; + }; + +EXEC SQL TYPE cust_ind IS + struct ind + { + short name_ind; + short phone_ind; + }; + +EXEC SQL TYPE c IS char reference; +EXEC SQL TYPE ind IS union { int integer; short smallint; }; +EXEC SQL TYPE intarray IS int[AMOUNT]; +EXEC SQL TYPE str IS varchar[BUFFERSIZ]; +EXEC SQL TYPE string IS char[11]; + + + + Here is an example program that uses EXEC SQL + TYPE: + +EXEC SQL WHENEVER SQLERROR SQLPRINT; + +EXEC SQL TYPE tt IS + struct + { + varchar v[256]; + int i; + }; + +EXEC SQL TYPE tt_ind IS + struct ind { + short v_ind; + short i_ind; + }; + +int +main(void) +{ +EXEC SQL BEGIN DECLARE SECTION; + tt t; + tt_ind t_ind; +EXEC SQL END DECLARE SECTION; + + EXEC SQL CONNECT TO testdb AS con1; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + + EXEC SQL SELECT current_database(), 256 INTO :t:t_ind LIMIT 1; + + printf("t.v = %s\n", t.v.arr); + printf("t.i = %d\n", t.i); + + printf("t_ind.v_ind = %d\n", t_ind.v_ind); + printf("t_ind.i_ind = %d\n", t_ind.i_ind); + + EXEC SQL DISCONNECT con1; + + return 0; +} + + + The output from this program looks like this: + +t.v = testdb +t.i = 256 +t_ind.v_ind = 0 +t_ind.i_ind = 0 + + + + + + Compatibility + + + The TYPE command is a PostgreSQL extension. + + + + + + + VAR + define a variable + + + + +VAR varname IS ctype + + + + + Description + + + The VAR command assigns a new C data type + to a host variable. The host variable must be previously + declared in a declare section. + + + + + Parameters + + + + varname + + + A C variable name. + + + + + + ctype + + + A C type specification. + + + + + + + + Examples + + +Exec sql begin declare section; +short a; +exec sql end declare section; +EXEC SQL VAR a IS int; + + + + + Compatibility + + + The VAR command is a PostgreSQL extension. + + + + + + + WHENEVER + specify the action to be taken when an SQL statement causes a specific class condition to be raised + + + + +WHENEVER { NOT FOUND | SQLERROR | SQLWARNING } action + + + + + Description + + + Define a behavior which is called on the special cases (Rows not + found, SQL warnings or errors) in the result of SQL execution. + + + + + Parameters + + + See for a description of the + parameters. + + + + + Examples + + +EXEC SQL WHENEVER NOT FOUND CONTINUE; +EXEC SQL WHENEVER NOT FOUND DO BREAK; +EXEC SQL WHENEVER NOT FOUND DO CONTINUE; +EXEC SQL WHENEVER SQLWARNING SQLPRINT; +EXEC SQL WHENEVER SQLWARNING DO warn(); +EXEC SQL WHENEVER SQLERROR sqlprint; +EXEC SQL WHENEVER SQLERROR CALL print2(); +EXEC SQL WHENEVER SQLERROR DO handle_error("select"); +EXEC SQL WHENEVER SQLERROR DO sqlnotice(NULL, NONO); +EXEC SQL WHENEVER SQLERROR DO sqlprint(); +EXEC SQL WHENEVER SQLERROR GOTO error_label; +EXEC SQL WHENEVER SQLERROR STOP; + + + + A typical application is the use of WHENEVER NOT FOUND + BREAK to handle looping through result sets: + +int +main(void) +{ + EXEC SQL CONNECT TO testdb AS con1; + EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT; + EXEC SQL ALLOCATE DESCRIPTOR d; + EXEC SQL DECLARE cur CURSOR FOR SELECT current_database(), 'hoge', 256; + EXEC SQL OPEN cur; + + /* when end of result set reached, break out of while loop */ + EXEC SQL WHENEVER NOT FOUND DO BREAK; + + while (1) + { + EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d; + ... + } + + EXEC SQL CLOSE cur; + EXEC SQL COMMIT; + + EXEC SQL DEALLOCATE DESCRIPTOR d; + EXEC SQL DISCONNECT ALL; + + return 0; +} + + + + + + Compatibility + + + WHENEVER is specified in the SQL standard, but + most of the actions are PostgreSQL extensions. + + + + + + + <productname>Informix</productname> Compatibility Mode + + ecpg can be run in a so-called Informix compatibility mode. If + this mode is active, it tries to behave as if it were the Informix + precompiler for Informix E/SQL. Generally spoken this will allow you to use + the dollar sign instead of the EXEC SQL primitive to introduce + embedded SQL commands: + +$int j = 3; +$CONNECT TO :dbname; +$CREATE TABLE test(i INT PRIMARY KEY, j INT); +$INSERT INTO test(i, j) VALUES (7, :j); +$COMMIT; + + + + + + There must not be any white space between the $ + and a following preprocessor directive, that is, + include, define, ifdef, + etc. Otherwise, the preprocessor will parse the token as a host + variable. + + + + + There are two compatibility modes: INFORMIX, INFORMIX_SE + + + When linking programs that use this compatibility mode, remember to link + against libcompat that is shipped with ECPG. + + + Besides the previously explained syntactic sugar, the Informix compatibility + mode ports some functions for input, output and transformation of data as + well as embedded SQL statements known from E/SQL to ECPG. + + + Informix compatibility mode is closely connected to the pgtypeslib library + of ECPG. pgtypeslib maps SQL data types to data types within the C host + program and most of the additional functions of the Informix compatibility + mode allow you to operate on those C host program types. Note however that + the extent of the compatibility is limited. It does not try to copy Informix + behavior; it allows you to do more or less the same operations and gives + you functions that have the same name and the same basic behavior but it is + no drop-in replacement if you are using Informix at the moment. Moreover, + some of the data types are different. For example, + PostgreSQL's datetime and interval types do not + know about ranges like for example YEAR TO MINUTE so you won't + find support in ECPG for that either. + + + + Additional Types + + The Informix-special "string" pseudo-type for storing right-trimmed character string data is now + supported in Informix-mode without using typedef. In fact, in Informix-mode, + ECPG refuses to process source files that contain typedef sometype string; + +EXEC SQL BEGIN DECLARE SECTION; +string userid; /* this variable will contain trimmed data */ +EXEC SQL END DECLARE SECTION; + +EXEC SQL FETCH MYCUR INTO :userid; + + + + + + Additional/Missing Embedded SQL Statements + + + + CLOSE DATABASE + + + This statement closes the current connection. In fact, this is a + synonym for ECPG's DISCONNECT CURRENT: + +$CLOSE DATABASE; /* close the current connection */ +EXEC SQL CLOSE DATABASE; + + + + + + FREE cursor_name + + + Due to the differences how ECPG works compared to Informix's ESQL/C (i.e., which steps + are purely grammar transformations and which steps rely on the underlying run-time library) + there is no FREE cursor_name statement in ECPG. This is because in ECPG, + DECLARE CURSOR doesn't translate to a function call into + the run-time library that uses to the cursor name. This means that there's no run-time + bookkeeping of SQL cursors in the ECPG run-time library, only in the PostgreSQL server. + + + + + FREE statement_name + + + FREE statement_name is a synonym for DEALLOCATE PREPARE statement_name. + + + + + + + + + Informix-compatible SQLDA Descriptor Areas + + Informix-compatible mode supports a different structure than the one described in + . See below: + +struct sqlvar_compat +{ + short sqltype; + int sqllen; + char *sqldata; + short *sqlind; + char *sqlname; + char *sqlformat; + short sqlitype; + short sqlilen; + char *sqlidata; + int sqlxid; + char *sqltypename; + short sqltypelen; + short sqlownerlen; + short sqlsourcetype; + char *sqlownername; + int sqlsourceid; + char *sqlilongdata; + int sqlflags; + void *sqlreserved; +}; + +struct sqlda_compat +{ + short sqld; + struct sqlvar_compat *sqlvar; + char desc_name[19]; + short desc_occ; + struct sqlda_compat *desc_next; + void *reserved; +}; + +typedef struct sqlvar_compat sqlvar_t; +typedef struct sqlda_compat sqlda_t; + + + + + The global properties are: + + + + sqld + + + The number of fields in the SQLDA descriptor. + + + + + + sqlvar + + + Pointer to the per-field properties. + + + + + + desc_name + + + Unused, filled with zero-bytes. + + + + + + desc_occ + + + Size of the allocated structure. + + + + + + desc_next + + + Pointer to the next SQLDA structure if the result set contains more than one record. + + + + + + reserved + + + Unused pointer, contains NULL. Kept for Informix-compatibility. + + + + + + + The per-field properties are below, they are stored in the sqlvar array: + + + + + sqltype + + + Type of the field. Constants are in sqltypes.h + + + + + + sqllen + + + Length of the field data. + + + + + + sqldata + + + Pointer to the field data. The pointer is of char * type, + the data pointed by it is in a binary format. Example: + +int intval; + +switch (sqldata->sqlvar[i].sqltype) +{ + case SQLINTEGER: + intval = *(int *)sqldata->sqlvar[i].sqldata; + break; + ... +} + + + + + + + sqlind + + + Pointer to the NULL indicator. If returned by DESCRIBE or FETCH then it's always a valid pointer. + If used as input for EXECUTE ... USING sqlda; then NULL-pointer value means + that the value for this field is non-NULL. Otherwise a valid pointer and sqlitype + has to be properly set. Example: + +if (*(int2 *)sqldata->sqlvar[i].sqlind != 0) + printf("value is NULL\n"); + + + + + + + sqlname + + + Name of the field. 0-terminated string. + + + + + + sqlformat + + + Reserved in Informix, value of for the field. + + + + + + sqlitype + + + Type of the NULL indicator data. It's always SQLSMINT when returning data from the server. + When the SQLDA is used for a parameterized query, the data is treated + according to the set type. + + + + + + sqlilen + + + Length of the NULL indicator data. + + + + + + sqlxid + + + Extended type of the field, result of . + + + + + + sqltypename + sqltypelen + sqlownerlen + sqlsourcetype + sqlownername + sqlsourceid + sqlflags + sqlreserved + + + Unused. + + + + + + sqlilongdata + + + It equals to sqldata if sqllen is larger than 32kB. + + + + + + + Example: + +EXEC SQL INCLUDE sqlda.h; + + sqlda_t *sqlda; /* This doesn't need to be under embedded DECLARE SECTION */ + + EXEC SQL BEGIN DECLARE SECTION; + char *prep_stmt = "select * from table1"; + int i; + EXEC SQL END DECLARE SECTION; + + ... + + EXEC SQL PREPARE mystmt FROM :prep_stmt; + + EXEC SQL DESCRIBE mystmt INTO sqlda; + + printf("# of fields: %d\n", sqlda->sqld); + for (i = 0; i < sqlda->sqld; i++) + printf("field %d: \"%s\"\n", sqlda->sqlvar[i]->sqlname); + + EXEC SQL DECLARE mycursor CURSOR FOR mystmt; + EXEC SQL OPEN mycursor; + EXEC SQL WHENEVER NOT FOUND GOTO out; + + while (1) + { + EXEC SQL FETCH mycursor USING sqlda; + } + + EXEC SQL CLOSE mycursor; + + free(sqlda); /* The main structure is all to be free(), + * sqlda and sqlda->sqlvar is in one allocated area */ + + For more information, see the sqlda.h header and the + src/interfaces/ecpg/test/compat_informix/sqlda.pgc regression test. + + + + + Additional Functions + + + + decadd + + + Add two decimal type values. + +int decadd(decimal *arg1, decimal *arg2, decimal *sum); + + The function receives a pointer to the first operand of type decimal + (arg1), a pointer to the second operand of type decimal + (arg2) and a pointer to a value of type decimal that will + contain the sum (sum). On success, the function returns 0. + ECPG_INFORMIX_NUM_OVERFLOW is returned in case of overflow and + ECPG_INFORMIX_NUM_UNDERFLOW in case of underflow. -1 is returned for + other failures and errno is set to the respective errno number of the + pgtypeslib. + + + + + + deccmp + + + Compare two variables of type decimal. + +int deccmp(decimal *arg1, decimal *arg2); + + The function receives a pointer to the first decimal value + (arg1), a pointer to the second decimal value + (arg2) and returns an integer value that indicates which is + the bigger value. + + + + 1, if the value that arg1 points to is bigger than the + value that var2 points to + + + + + -1, if the value that arg1 points to is smaller than the + value that arg2 points to + + + + 0, if the value that arg1 points to and the value that + arg2 points to are equal + + + + + + + + + deccopy + + + Copy a decimal value. + +void deccopy(decimal *src, decimal *target); + + The function receives a pointer to the decimal value that should be + copied as the first argument (src) and a pointer to the + target structure of type decimal (target) as the second + argument. + + + + + + deccvasc + + + Convert a value from its ASCII representation into a decimal type. + +int deccvasc(char *cp, int len, decimal *np); + + The function receives a pointer to string that contains the string + representation of the number to be converted (cp) as well + as its length len. np is a pointer to the + decimal value that saves the result of the operation. + + + Valid formats are for example: + -2, + .794, + +3.44, + 592.49E07 or + -32.84e-4. + + + The function returns 0 on success. If overflow or underflow occurred, + ECPG_INFORMIX_NUM_OVERFLOW or + ECPG_INFORMIX_NUM_UNDERFLOW is returned. If the ASCII + representation could not be parsed, + ECPG_INFORMIX_BAD_NUMERIC is returned or + ECPG_INFORMIX_BAD_EXPONENT if this problem occurred while + parsing the exponent. + + + + + + deccvdbl + + + Convert a value of type double to a value of type decimal. + +int deccvdbl(double dbl, decimal *np); + + The function receives the variable of type double that should be + converted as its first argument (dbl). As the second + argument (np), the function receives a pointer to the + decimal variable that should hold the result of the operation. + + + The function returns 0 on success and a negative value if the + conversion failed. + + + + + + deccvint + + + Convert a value of type int to a value of type decimal. + +int deccvint(int in, decimal *np); + + The function receives the variable of type int that should be + converted as its first argument (in). As the second + argument (np), the function receives a pointer to the + decimal variable that should hold the result of the operation. + + + The function returns 0 on success and a negative value if the + conversion failed. + + + + + + deccvlong + + + Convert a value of type long to a value of type decimal. + +int deccvlong(long lng, decimal *np); + + The function receives the variable of type long that should be + converted as its first argument (lng). As the second + argument (np), the function receives a pointer to the + decimal variable that should hold the result of the operation. + + + The function returns 0 on success and a negative value if the + conversion failed. + + + + + + decdiv + + + Divide two variables of type decimal. + +int decdiv(decimal *n1, decimal *n2, decimal *result); + + The function receives pointers to the variables that are the first + (n1) and the second (n2) operands and + calculates n1/n2. result is a + pointer to the variable that should hold the result of the operation. + + + On success, 0 is returned and a negative value if the division fails. + If overflow or underflow occurred, the function returns + ECPG_INFORMIX_NUM_OVERFLOW or + ECPG_INFORMIX_NUM_UNDERFLOW respectively. If an attempt to + divide by zero is observed, the function returns + ECPG_INFORMIX_DIVIDE_ZERO. + + + + + + decmul + + + Multiply two decimal values. + +int decmul(decimal *n1, decimal *n2, decimal *result); + + The function receives pointers to the variables that are the first + (n1) and the second (n2) operands and + calculates n1*n2. result is a + pointer to the variable that should hold the result of the operation. + + + On success, 0 is returned and a negative value if the multiplication + fails. If overflow or underflow occurred, the function returns + ECPG_INFORMIX_NUM_OVERFLOW or + ECPG_INFORMIX_NUM_UNDERFLOW respectively. + + + + + + decsub + + + Subtract one decimal value from another. + +int decsub(decimal *n1, decimal *n2, decimal *result); + + The function receives pointers to the variables that are the first + (n1) and the second (n2) operands and + calculates n1-n2. result is a + pointer to the variable that should hold the result of the operation. + + + On success, 0 is returned and a negative value if the subtraction + fails. If overflow or underflow occurred, the function returns + ECPG_INFORMIX_NUM_OVERFLOW or + ECPG_INFORMIX_NUM_UNDERFLOW respectively. + + + + + + dectoasc + + + Convert a variable of type decimal to its ASCII representation in a C + char* string. + +int dectoasc(decimal *np, char *cp, int len, int right) + + The function receives a pointer to a variable of type decimal + (np) that it converts to its textual representation. + cp is the buffer that should hold the result of the + operation. The parameter right specifies, how many digits + right of the decimal point should be included in the output. The result + will be rounded to this number of decimal digits. Setting + right to -1 indicates that all available decimal digits + should be included in the output. If the length of the output buffer, + which is indicated by len is not sufficient to hold the + textual representation including the trailing zero byte, only a + single * character is stored in the result and -1 is + returned. + + + The function returns either -1 if the buffer cp was too + small or ECPG_INFORMIX_OUT_OF_MEMORY if memory was + exhausted. + + + + + + dectodbl + + + Convert a variable of type decimal to a double. + +int dectodbl(decimal *np, double *dblp); + + The function receives a pointer to the decimal value to convert + (np) and a pointer to the double variable that + should hold the result of the operation (dblp). + + + On success, 0 is returned and a negative value if the conversion + failed. + + + + + + dectoint + + + Convert a variable to type decimal to an integer. + +int dectoint(decimal *np, int *ip); + + The function receives a pointer to the decimal value to convert + (np) and a pointer to the integer variable that + should hold the result of the operation (ip). + + + On success, 0 is returned and a negative value if the conversion + failed. If an overflow occurred, ECPG_INFORMIX_NUM_OVERFLOW + is returned. + + + Note that the ECPG implementation differs from the Informix + implementation. Informix limits an integer to the range from -32767 to + 32767, while the limits in the ECPG implementation depend on the + architecture (INT_MIN .. INT_MAX). + + + + + + dectolong + + + Convert a variable to type decimal to a long integer. + +int dectolong(decimal *np, long *lngp); + + The function receives a pointer to the decimal value to convert + (np) and a pointer to the long variable that + should hold the result of the operation (lngp). + + + On success, 0 is returned and a negative value if the conversion + failed. If an overflow occurred, ECPG_INFORMIX_NUM_OVERFLOW + is returned. + + + Note that the ECPG implementation differs from the Informix + implementation. Informix limits a long integer to the range from + -2,147,483,647 to 2,147,483,647, while the limits in the ECPG + implementation depend on the architecture (-LONG_MAX .. + LONG_MAX). + + + + + + rdatestr + + + Converts a date to a C char* string. + +int rdatestr(date d, char *str); + + The function receives two arguments, the first one is the date to + convert (d) and the second one is a pointer to the target + string. The output format is always yyyy-mm-dd, so you need + to allocate at least 11 bytes (including the zero-byte terminator) for the + string. + + + The function returns 0 on success and a negative value in case of + error. + + + Note that ECPG's implementation differs from the Informix + implementation. In Informix the format can be influenced by setting + environment variables. In ECPG however, you cannot change the output + format. + + + + + + rstrdate + + + Parse the textual representation of a date. + +int rstrdate(char *str, date *d); + + The function receives the textual representation of the date to convert + (str) and a pointer to a variable of type date + (d). This function does not allow you to specify a format + mask. It uses the default format mask of Informix which is + mm/dd/yyyy. Internally, this function is implemented by + means of rdefmtdate. Therefore, rstrdate is + not faster and if you have the choice you should opt for + rdefmtdate which allows you to specify the format mask + explicitly. + + + The function returns the same values as rdefmtdate. + + + + + + rtoday + + + Get the current date. + +void rtoday(date *d); + + The function receives a pointer to a date variable (d) + that it sets to the current date. + + + Internally this function uses the + function. + + + + + + rjulmdy + + + Extract the values for the day, the month and the year from a variable + of type date. + +int rjulmdy(date d, short mdy[3]); + + The function receives the date d and a pointer to an array + of 3 short integer values mdy. The variable name indicates + the sequential order: mdy[0] will be set to contain the + number of the month, mdy[1] will be set to the value of the + day and mdy[2] will contain the year. + + + The function always returns 0 at the moment. + + + Internally the function uses the + function. + + + + + + rdefmtdate + + + Use a format mask to convert a character string to a value of type + date. + +int rdefmtdate(date *d, char *fmt, char *str); + + The function receives a pointer to the date value that should hold the + result of the operation (d), the format mask to use for + parsing the date (fmt) and the C char* string containing + the textual representation of the date (str). The textual + representation is expected to match the format mask. However you do not + need to have a 1:1 mapping of the string to the format mask. The + function only analyzes the sequential order and looks for the literals + yy or yyyy that indicate the + position of the year, mm to indicate the position of + the month and dd to indicate the position of the + day. + + + The function returns the following values: + + + + 0 - The function terminated successfully. + + + + + ECPG_INFORMIX_ENOSHORTDATE - The date does not contain + delimiters between day, month and year. In this case the input + string must be exactly 6 or 8 bytes long but isn't. + + + + + ECPG_INFORMIX_ENOTDMY - The format string did not + correctly indicate the sequential order of year, month and day. + + + + + ECPG_INFORMIX_BAD_DAY - The input string does not + contain a valid day. + + + + + ECPG_INFORMIX_BAD_MONTH - The input string does not + contain a valid month. + + + + + ECPG_INFORMIX_BAD_YEAR - The input string does not + contain a valid year. + + + + + + Internally this function is implemented to use the function. See the reference there for a + table of example input. + + + + + + rfmtdate + + + Convert a variable of type date to its textual representation using a + format mask. + +int rfmtdate(date d, char *fmt, char *str); + + The function receives the date to convert (d), the format + mask (fmt) and the string that will hold the textual + representation of the date (str). + + + On success, 0 is returned and a negative value if an error occurred. + + + Internally this function uses the + function, see the reference there for examples. + + + + + + rmdyjul + + + Create a date value from an array of 3 short integers that specify the + day, the month and the year of the date. + +int rmdyjul(short mdy[3], date *d); + + The function receives the array of the 3 short integers + (mdy) and a pointer to a variable of type date that should + hold the result of the operation. + + + Currently the function returns always 0. + + + Internally the function is implemented to use the function . + + + + + + rdayofweek + + + Return a number representing the day of the week for a date value. + +int rdayofweek(date d); + + The function receives the date variable d as its only + argument and returns an integer that indicates the day of the week for + this date. + + + + 0 - Sunday + + + + + 1 - Monday + + + + + 2 - Tuesday + + + + + 3 - Wednesday + + + + + 4 - Thursday + + + + + 5 - Friday + + + + + 6 - Saturday + + + + + + Internally the function is implemented to use the function . + + + + + + dtcurrent + + + Retrieve the current timestamp. + +void dtcurrent(timestamp *ts); + + The function retrieves the current timestamp and saves it into the + timestamp variable that ts points to. + + + + + + dtcvasc + + + Parses a timestamp from its textual representation + into a timestamp variable. + +int dtcvasc(char *str, timestamp *ts); + + The function receives the string to parse (str) and a + pointer to the timestamp variable that should hold the result of the + operation (ts). + + + The function returns 0 on success and a negative value in case of + error. + + + Internally this function uses the function. See the reference there + for a table with example inputs. + + + + + + dtcvfmtasc + + + Parses a timestamp from its textual representation + using a format mask into a timestamp variable. + +dtcvfmtasc(char *inbuf, char *fmtstr, timestamp *dtvalue) + + The function receives the string to parse (inbuf), the + format mask to use (fmtstr) and a pointer to the timestamp + variable that should hold the result of the operation + (dtvalue). + + + This function is implemented by means of the function. See the documentation + there for a list of format specifiers that can be used. + + + The function returns 0 on success and a negative value in case of + error. + + + + + + dtsub + + + Subtract one timestamp from another and return a variable of type + interval. + +int dtsub(timestamp *ts1, timestamp *ts2, interval *iv); + + The function will subtract the timestamp variable that ts2 + points to from the timestamp variable that ts1 points to + and will store the result in the interval variable that iv + points to. + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + + + + dttoasc + + + Convert a timestamp variable to a C char* string. + +int dttoasc(timestamp *ts, char *output); + + The function receives a pointer to the timestamp variable to convert + (ts) and the string that should hold the result of the + operation (output). It converts ts to its + textual representation according to the SQL standard, which is + be YYYY-MM-DD HH:MM:SS. + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + + + + dttofmtasc + + + Convert a timestamp variable to a C char* using a format mask. + +int dttofmtasc(timestamp *ts, char *output, int str_len, char *fmtstr); + + The function receives a pointer to the timestamp to convert as its + first argument (ts), a pointer to the output buffer + (output), the maximal length that has been allocated for + the output buffer (str_len) and the format mask to + use for the conversion (fmtstr). + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + Internally, this function uses the function. See the reference there for + information on what format mask specifiers can be used. + + + + + + intoasc + + + Convert an interval variable to a C char* string. + +int intoasc(interval *i, char *str); + + The function receives a pointer to the interval variable to convert + (i) and the string that should hold the result of the + operation (str). It converts i to its + textual representation according to the SQL standard, which is + be YYYY-MM-DD HH:MM:SS. + + + Upon success, the function returns 0 and a negative value if an + error occurred. + + + + + + rfmtlong + + + Convert a long integer value to its textual representation using a + format mask. + +int rfmtlong(long lng_val, char *fmt, char *outbuf); + + The function receives the long value lng_val, the format + mask fmt and a pointer to the output buffer + outbuf. It converts the long value according to the format + mask to its textual representation. + + + The format mask can be composed of the following format specifying + characters: + + + + * (asterisk) - if this position would be blank + otherwise, fill it with an asterisk. + + + + + & (ampersand) - if this position would be + blank otherwise, fill it with a zero. + + + + + # - turn leading zeroes into blanks. + + + + + < - left-justify the number in the string. + + + + + , (comma) - group numbers of four or more digits + into groups of three digits separated by a comma. + + + + + . (period) - this character separates the + whole-number part of the number from the fractional part. + + + + + - (minus) - the minus sign appears if the number + is a negative value. + + + + + + (plus) - the plus sign appears if the number is + a positive value. + + + + + ( - this replaces the minus sign in front of the + negative number. The minus sign will not appear. + + + + + ) - this character replaces the minus and is + printed behind the negative value. + + + + + $ - the currency symbol. + + + + + + + + + rupshift + + + Convert a string to upper case. + +void rupshift(char *str); + + The function receives a pointer to the string and transforms every + lower case character to upper case. + + + + + + byleng + + + Return the number of characters in a string without counting trailing + blanks. + +int byleng(char *str, int len); + + The function expects a fixed-length string as its first argument + (str) and its length as its second argument + (len). It returns the number of significant characters, + that is the length of the string without trailing blanks. + + + + + + ldchar + + + Copy a fixed-length string into a null-terminated string. + +void ldchar(char *src, int len, char *dest); + + The function receives the fixed-length string to copy + (src), its length (len) and a pointer to the + destination memory (dest). Note that you need to reserve at + least len+1 bytes for the string that dest + points to. The function copies at most len bytes to the new + location (less if the source string has trailing blanks) and adds the + null-terminator. + + + + + + rgetmsg + + + +int rgetmsg(int msgnum, char *s, int maxsize); + + This function exists but is not implemented at the moment! + + + + + + rtypalign + + + +int rtypalign(int offset, int type); + + This function exists but is not implemented at the moment! + + + + + + rtypmsize + + + +int rtypmsize(int type, int len); + + This function exists but is not implemented at the moment! + + + + + + rtypwidth + + + +int rtypwidth(int sqltype, int sqllen); + + This function exists but is not implemented at the moment! + + + + + + rsetnull + + + Set a variable to NULL. + +int rsetnull(int t, char *ptr); + + The function receives an integer that indicates the type of the + variable and a pointer to the variable itself that is cast to a C + char* pointer. + + + The following types exist: + + + + CCHARTYPE - For a variable of type char or char* + + + + + CSHORTTYPE - For a variable of type short int + + + + + CINTTYPE - For a variable of type int + + + + + CBOOLTYPE - For a variable of type boolean + + + + + CFLOATTYPE - For a variable of type float + + + + + CLONGTYPE - For a variable of type long + + + + + CDOUBLETYPE - For a variable of type double + + + + + CDECIMALTYPE - For a variable of type decimal + + + + + CDATETYPE - For a variable of type date + + + + + CDTIMETYPE - For a variable of type timestamp + + + + + + + Here is an example of a call to this function: + + + + + + + + risnull + + + Test if a variable is NULL. + +int risnull(int t, char *ptr); + + The function receives the type of the variable to test (t) + as well a pointer to this variable (ptr). Note that the + latter needs to be cast to a char*. See the function for a list of possible variable types. + + + Here is an example of how to use this function: + + + + + + + + + + + Additional Constants + + Note that all constants here describe errors and all of them are defined + to represent negative values. In the descriptions of the different + constants you can also find the value that the constants represent in the + current implementation. However you should not rely on this number. You can + however rely on the fact all of them are defined to represent negative + values. + + + ECPG_INFORMIX_NUM_OVERFLOW + + + Functions return this value if an overflow occurred in a + calculation. Internally it is defined as -1200 (the Informix + definition). + + + + + + ECPG_INFORMIX_NUM_UNDERFLOW + + + Functions return this value if an underflow occurred in a calculation. + Internally it is defined as -1201 (the Informix definition). + + + + + + ECPG_INFORMIX_DIVIDE_ZERO + + + Functions return this value if an attempt to divide by zero is + observed. Internally it is defined as -1202 (the Informix definition). + + + + + + ECPG_INFORMIX_BAD_YEAR + + + Functions return this value if a bad value for a year was found while + parsing a date. Internally it is defined as -1204 (the Informix + definition). + + + + + + ECPG_INFORMIX_BAD_MONTH + + + Functions return this value if a bad value for a month was found while + parsing a date. Internally it is defined as -1205 (the Informix + definition). + + + + + + ECPG_INFORMIX_BAD_DAY + + + Functions return this value if a bad value for a day was found while + parsing a date. Internally it is defined as -1206 (the Informix + definition). + + + + + + ECPG_INFORMIX_ENOSHORTDATE + + + Functions return this value if a parsing routine needs a short date + representation but did not get the date string in the right length. + Internally it is defined as -1209 (the Informix definition). + + + + + + ECPG_INFORMIX_DATE_CONVERT + + + Functions return this value if an error occurred during date + formatting. Internally it is defined as -1210 (the + Informix definition). + + + + + + ECPG_INFORMIX_OUT_OF_MEMORY + + + Functions return this value if memory was exhausted during + their operation. Internally it is defined as -1211 (the + Informix definition). + + + + + + ECPG_INFORMIX_ENOTDMY + + + Functions return this value if a parsing routine was supposed to get a + format mask (like mmddyy) but not all fields were listed + correctly. Internally it is defined as -1212 (the Informix definition). + + + + + + ECPG_INFORMIX_BAD_NUMERIC + + + Functions return this value either if a parsing routine cannot parse + the textual representation for a numeric value because it contains + errors or if a routine cannot complete a calculation involving numeric + variables because at least one of the numeric variables is invalid. + Internally it is defined as -1213 (the Informix definition). + + + + + + ECPG_INFORMIX_BAD_EXPONENT + + + Functions return this value if a parsing routine cannot parse + an exponent. Internally it is defined as -1216 (the + Informix definition). + + + + + + ECPG_INFORMIX_BAD_DATE + + + Functions return this value if a parsing routine cannot parse + a date. Internally it is defined as -1218 (the + Informix definition). + + + + + + ECPG_INFORMIX_EXTRA_CHARS + + + Functions return this value if a parsing routine is passed extra + characters it cannot parse. Internally it is defined as -1264 (the + Informix definition). + + + + + + + + + + Internals + + + This section explains how ECPG works + internally. This information can occasionally be useful to help + users understand how to use ECPG. + + + + The first four lines written by ecpg to the + output are fixed lines. Two are comments and two are include + lines necessary to interface to the library. Then the + preprocessor reads through the file and writes output. Normally + it just echoes everything to the output. + + + + When it sees an EXEC SQL statement, it + intervenes and changes it. The command starts with EXEC + SQL and ends with ;. Everything in + between is treated as an SQL statement and + parsed for variable substitution. + + + + Variable substitution occurs when a symbol starts with a colon + (:). The variable with that name is looked up + among the variables that were previously declared within a + EXEC SQL DECLARE section. + + + + The most important function in the library is + ECPGdo, which takes care of executing most + commands. It takes a variable number of arguments. This can easily + add up to 50 or so arguments, and we hope this will not be a + problem on any platform. + + + + The arguments are: + + + + A line number + + + This is the line number of the original line; used in error + messages only. + + + + + + A string + + + This is the SQL command that is to be issued. + It is modified by the input variables, i.e., the variables that + where not known at compile time but are to be entered in the + command. Where the variables should go the string contains + ?. + + + + + + Input variables + + + Every input variable causes ten arguments to be created. (See below.) + + + + + + ECPGt_EOIT + + + An enum telling that there are no more input + variables. + + + + + + Output variables + + + Every output variable causes ten arguments to be created. + (See below.) These variables are filled by the function. + + + + + + ECPGt_EORT + + + An enum telling that there are no more variables. + + + + + + + + For every variable that is part of the SQL + command, the function gets ten arguments: + + + + + The type as a special symbol. + + + + + + A pointer to the value or a pointer to the pointer. + + + + + + The size of the variable if it is a char or varchar. + + + + + + The number of elements in the array (for array fetches). + + + + + + The offset to the next element in the array (for array fetches). + + + + + + The type of the indicator variable as a special symbol. + + + + + + A pointer to the indicator variable. + + + + + + 0 + + + + + + The number of elements in the indicator array (for array fetches). + + + + + + The offset to the next element in the indicator array (for + array fetches). + + + + + + + Note that not all SQL commands are treated in this way. For + instance, an open cursor statement like: + +EXEC SQL OPEN cursor; + + is not copied to the output. Instead, the cursor's + DECLARE command is used at the position of the OPEN command + because it indeed opens the cursor. + + + + Here is a complete example describing the output of the + preprocessor of a file foo.pgc (details might + change with each particular version of the preprocessor): + +EXEC SQL BEGIN DECLARE SECTION; +int index; +int result; +EXEC SQL END DECLARE SECTION; +... +EXEC SQL SELECT res INTO :result FROM mytable WHERE index = :index; + + is translated into: +; +#include ; + +/* exec sql begin declare section */ + +#line 1 "foo.pgc" + + int index; + int result; +/* exec sql end declare section */ +... +ECPGdo(__LINE__, NULL, "SELECT res FROM mytable WHERE index = ? ", + ECPGt_int,&(index),1L,1L,sizeof(int), + ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EOIT, + ECPGt_int,&(result),1L,1L,sizeof(int), + ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT); +#line 147 "foo.pgc" +]]> + + (The indentation here is added for readability and not + something the preprocessor does.) + + + -- cgit v1.2.3