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diff --git a/doc/src/sgml/html/ecpg-preproc.html b/doc/src/sgml/html/ecpg-preproc.html new file mode 100644 index 0000000..951dbf3 --- /dev/null +++ b/doc/src/sgml/html/ecpg-preproc.html @@ -0,0 +1,129 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>36.9. Preprocessor Directives</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="ecpg-errors.html" title="36.8. Error Handling" /><link rel="next" href="ecpg-process.html" title="36.10. Processing Embedded SQL Programs" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">36.9. Preprocessor Directives</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ecpg-errors.html" title="36.8. Error Handling">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Up</a></td><th width="60%" align="center">Chapter 36. <span class="application">ECPG</span> — Embedded <acronym class="acronym">SQL</acronym> in C</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ecpg-process.html" title="36.10. Processing Embedded SQL Programs">Next</a></td></tr></table><hr /></div><div class="sect1" id="ECPG-PREPROC"><div class="titlepage"><div><div><h2 class="title" style="clear: both">36.9. Preprocessor Directives</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="ecpg-preproc.html#ECPG-INCLUDE">36.9.1. Including Files</a></span></dt><dt><span class="sect2"><a href="ecpg-preproc.html#ECPG-DEFINE">36.9.2. The define and undef Directives</a></span></dt><dt><span class="sect2"><a href="ecpg-preproc.html#ECPG-IFDEF">36.9.3. ifdef, ifndef, elif, else, and endif Directives</a></span></dt></dl></div><p> + Several preprocessor directives are available that modify how + the <code class="command">ecpg</code> preprocessor parses and processes a + file. + </p><div class="sect2" id="ECPG-INCLUDE"><div class="titlepage"><div><div><h3 class="title">36.9.1. Including Files</h3></div></div></div><p> + To include an external file into your embedded SQL program, use: +</p><pre class="programlisting"> +EXEC SQL INCLUDE <em class="replaceable"><code>filename</code></em>; +EXEC SQL INCLUDE <<em class="replaceable"><code>filename</code></em>>; +EXEC SQL INCLUDE "<em class="replaceable"><code>filename</code></em>"; +</pre><p> + The embedded SQL preprocessor will look for a file named + <code class="literal"><em class="replaceable"><code>filename</code></em>.h</code>, + preprocess it, and include it in the resulting C output. Thus, + embedded SQL statements in the included file are handled correctly. + </p><p> + The <code class="command">ecpg</code> preprocessor will search a file at + several directories in following order: + + </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">current directory</li><li class="listitem"><code class="filename">/usr/local/include</code></li><li class="listitem">PostgreSQL include directory, defined at build time (e.g., <code class="filename">/usr/local/pgsql/include</code>)</li><li class="listitem"><code class="filename">/usr/include</code></li></ul></div><p> + + But when <code class="literal">EXEC SQL INCLUDE + "<em class="replaceable"><code>filename</code></em>"</code> is used, only the + current directory is searched. + </p><p> + In each directory, the preprocessor will first look for the file + name as given, and if not found will append <code class="literal">.h</code> + to the file name and try again (unless the specified file name + already has that suffix). + </p><p> + Note that <code class="command">EXEC SQL INCLUDE</code> is <span class="emphasis"><em>not</em></span> the same as: +</p><pre class="programlisting"> +#include <<em class="replaceable"><code>filename</code></em>.h> +</pre><p> + because this file would not be subject to SQL command preprocessing. + Naturally, you can continue to use the C + <code class="literal">#include</code> directive to include other header + files. + </p><div class="note"><h3 class="title">Note</h3><p> + The include file name is case-sensitive, even though the rest of + the <code class="literal">EXEC SQL INCLUDE</code> command follows the normal + SQL case-sensitivity rules. + </p></div></div><div class="sect2" id="ECPG-DEFINE"><div class="titlepage"><div><div><h3 class="title">36.9.2. The define and undef Directives</h3></div></div></div><p> + Similar to the directive <code class="literal">#define</code> that is known from C, + embedded SQL has a similar concept: +</p><pre class="programlisting"> +EXEC SQL DEFINE <em class="replaceable"><code>name</code></em>; +EXEC SQL DEFINE <em class="replaceable"><code>name</code></em> <em class="replaceable"><code>value</code></em>; +</pre><p> + So you can define a name: +</p><pre class="programlisting"> +EXEC SQL DEFINE HAVE_FEATURE; +</pre><p> + And you can also define constants: +</p><pre class="programlisting"> +EXEC SQL DEFINE MYNUMBER 12; +EXEC SQL DEFINE MYSTRING 'abc'; +</pre><p> + Use <code class="literal">undef</code> to remove a previous definition: +</p><pre class="programlisting"> +EXEC SQL UNDEF MYNUMBER; +</pre><p> + </p><p> + Of course you can continue to use the C versions <code class="literal">#define</code> + and <code class="literal">#undef</code> in your embedded SQL program. The difference + is where your defined values get evaluated. If you use <code class="literal">EXEC SQL + DEFINE</code> then the <code class="command">ecpg</code> preprocessor evaluates the defines and substitutes + the values. For example if you write: +</p><pre class="programlisting"> +EXEC SQL DEFINE MYNUMBER 12; +... +EXEC SQL UPDATE Tbl SET col = MYNUMBER; +</pre><p> + then <code class="command">ecpg</code> will already do the substitution and your C compiler will never + see any name or identifier <code class="literal">MYNUMBER</code>. Note that you cannot use + <code class="literal">#define</code> 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. + </p></div><div class="sect2" id="ECPG-IFDEF"><div class="titlepage"><div><div><h3 class="title">36.9.3. ifdef, ifndef, elif, else, and endif Directives</h3></div></div></div><p> + You can use the following directives to compile code sections conditionally: + + </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">EXEC SQL ifdef <em class="replaceable"><code>name</code></em>;</code></span></dt><dd><p> + Checks a <em class="replaceable"><code>name</code></em> and processes subsequent lines if + <em class="replaceable"><code>name</code></em> has been defined via <code class="literal">EXEC SQL define + <em class="replaceable"><code>name</code></em></code>. + </p></dd><dt><span class="term"><code class="literal">EXEC SQL ifndef <em class="replaceable"><code>name</code></em>;</code></span></dt><dd><p> + Checks a <em class="replaceable"><code>name</code></em> and processes subsequent lines if + <em class="replaceable"><code>name</code></em> has <span class="emphasis"><em>not</em></span> been defined via + <code class="literal">EXEC SQL define <em class="replaceable"><code>name</code></em></code>. + </p></dd><dt><span class="term"><code class="literal">EXEC SQL elif <em class="replaceable"><code>name</code></em>;</code></span></dt><dd><p> + Begins an optional alternative section after an + <code class="literal">EXEC SQL ifdef <em class="replaceable"><code>name</code></em></code> or + <code class="literal">EXEC SQL ifndef <em class="replaceable"><code>name</code></em></code> + directive. Any number of <code class="literal">elif</code> sections can appear. + Lines following an <code class="literal">elif</code> will be processed + if <em class="replaceable"><code>name</code></em> has been + defined <span class="emphasis"><em>and</em></span> no previous section of the same + <code class="literal">ifdef</code>/<code class="literal">ifndef</code>...<code class="literal">endif</code> + construct has been processed. + </p></dd><dt><span class="term"><code class="literal">EXEC SQL else;</code></span></dt><dd><p> + Begins an optional, final alternative section after an + <code class="literal">EXEC SQL ifdef <em class="replaceable"><code>name</code></em></code> or + <code class="literal">EXEC SQL ifndef <em class="replaceable"><code>name</code></em></code> + directive. Subsequent lines will be processed if no previous section + of the same + <code class="literal">ifdef</code>/<code class="literal">ifndef</code>...<code class="literal">endif</code> + construct has been processed. + </p></dd><dt><span class="term"><code class="literal">EXEC SQL endif;</code></span></dt><dd><p> + Ends an + <code class="literal">ifdef</code>/<code class="literal">ifndef</code>...<code class="literal">endif</code> + construct. Subsequent lines are processed normally. + </p></dd></dl></div><p> + </p><p> + <code class="literal">ifdef</code>/<code class="literal">ifndef</code>...<code class="literal">endif</code> + constructs can be nested, up to 127 levels deep. + </p><p> + This example will compile exactly one of the three <code class="literal">SET + TIMEZONE</code> commands: +</p><pre class="programlisting"> +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; +</pre><p> + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ecpg-errors.html" title="36.8. Error Handling">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg-process.html" title="36.10. 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