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diff --git a/www/c3ref/free_table.html b/www/c3ref/free_table.html new file mode 100644 index 0000000..9c08c28 --- /dev/null +++ b/www/c3ref/free_table.html @@ -0,0 +1,207 @@ +<!DOCTYPE html> +<html><head> +<meta name="viewport" content="width=device-width, initial-scale=1.0"> +<meta http-equiv="content-type" content="text/html; charset=UTF-8"> +<link href="../sqlite.css" rel="stylesheet"> +<title>Convenience Routines For Running Queries</title> +<!-- path=../ --> +</head> +<body> +<div class=nosearch> +<a href="../index.html"> +<img class="logo" src="../images/sqlite370_banner.gif" alt="SQLite" border="0"> +</a> +<div><!-- IE hack to prevent disappearing logo --></div> +<div class="tagline desktoponly"> +Small. Fast. 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A result table records the +complete query results from one or more queries.</p> + +<p>The table conceptually has a number of rows and columns. But +these numbers are not part of the result table itself. These +numbers are obtained separately. Let N be the number of rows +and M be the number of columns.</p> + +<p>A result table is an array of pointers to zero-terminated UTF-8 strings. +There are (N+1)*M elements in the array. The first M pointers point +to zero-terminated strings that contain the names of the columns. +The remaining entries all point to query results. NULL values result +in NULL pointers. All other values are in their UTF-8 zero-terminated +string representation as returned by <a href="../c3ref/column_blob.html">sqlite3_column_text()</a>.</p> + +<p>A result table might consist of one or more memory allocations. +It is not safe to pass a result table directly to <a href="../c3ref/free.html">sqlite3_free()</a>. +A result table should be deallocated using <a href="../c3ref/free_table.html">sqlite3_free_table()</a>.</p> + +<p>As an example of the result table format, suppose a query result +is as follows:</p> + +<p><blockquote><pre> +Name | Age +----------------------- +Alice | 43 +Bob | 28 +Cindy | 21 +</pre></blockquote></p> + +<p>There are two columns (M==2) and three rows (N==3). Thus the +result table has 8 entries. Suppose the result table is stored +in an array named azResult. Then azResult holds this content:</p> + +<p><blockquote><pre> +azResult[0] = "Name"; +azResult[1] = "Age"; +azResult[2] = "Alice"; +azResult[3] = "43"; +azResult[4] = "Bob"; +azResult[5] = "28"; +azResult[6] = "Cindy"; +azResult[7] = "21"; +</pre></blockquote></p> + +<p>The sqlite3_get_table() function evaluates one or more +semicolon-separated SQL statements in the zero-terminated UTF-8 +string of its 2nd parameter and returns a result table to the +pointer given in its 3rd parameter.</p> + +<p>After the application has finished with the result from sqlite3_get_table(), +it must pass the result table pointer to sqlite3_free_table() in order to +release the memory that was malloced. Because of the way the +<a href="../c3ref/free.html">sqlite3_malloc()</a> happens within sqlite3_get_table(), the calling +function must not try to call <a href="../c3ref/free.html">sqlite3_free()</a> directly. Only +<a href="../c3ref/free_table.html">sqlite3_free_table()</a> is able to release the memory properly and safely.</p> + +<p>The sqlite3_get_table() interface is implemented as a wrapper around +<a href="../c3ref/exec.html">sqlite3_exec()</a>. The sqlite3_get_table() routine does not have access +to any internal data structures of SQLite. It uses only the public +interface defined here. As a consequence, errors that occur in the +wrapper layer outside of the internal <a href="../c3ref/exec.html">sqlite3_exec()</a> call are not +reflected in subsequent calls to <a href="../c3ref/errcode.html">sqlite3_errcode()</a> or +<a href="../c3ref/errcode.html">sqlite3_errmsg()</a>. +</p><p>See also lists of + <a href="objlist.html">Objects</a>, + <a href="constlist.html">Constants</a>, and + <a href="funclist.html">Functions</a>.</p> + |