Adding upstream version 16.2.upstream/16.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-04-13 13:44:03 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-04-13 13:44:03 +0000
commit: 293913568e6a7a86fd1479e1cff8e2ecb58d6568 (patch)
tree: fc3b469a3ec5ab71b36ea97cc7aaddb838423a0c /doc/src/sgml/html/ecpg-preproc.html
parent: Initial commit. (diff)
download: postgresql-16-293913568e6a7a86fd1479e1cff8e2ecb58d6568.tar.xz
postgresql-16-293913568e6a7a86fd1479e1cff8e2ecb58d6568.zip
1 files changed, 129 insertions, 0 deletions
diff --git a/doc/src/sgml/html/ecpg-preproc.html b/doc/src/sgml/html/ecpg-preproc.html
new file mode 100644
index 0000000..0ec7bb5
--- /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 16.2 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 <a href="#ECPG-PREPROC" class="id_link">#</a></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 <a href="#ECPG-INCLUDE" class="id_link">#</a></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 &lt;<em class="replaceable"><code>filename</code></em>&gt;;
+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 &lt;<em class="replaceable"><code>filename</code></em>.h&gt;
+</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 <a href="#ECPG-DEFINE" class="id_link">#</a></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 <a href="#ECPG-IFDEF" class="id_link">#</a></h3></div></div></div><p>
+   You can use the following directives to compile code sections conditionally:
+
+   </p><div class="variablelist"><dl class="variablelist"><dt id="ECPG-IFDEF-IFDEF"><span class="term"><code class="literal">EXEC SQL ifdef <em class="replaceable"><code>name</code></em>;</code></span> <a href="#ECPG-IFDEF-IFDEF" class="id_link">#</a></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 id="ECPG-IFDEF-IFNDEF"><span class="term"><code class="literal">EXEC SQL ifndef <em class="replaceable"><code>name</code></em>;</code></span> <a href="#ECPG-IFDEF-IFNDEF" class="id_link">#</a></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 id="ECPG-IFDEF-ELIF"><span class="term"><code class="literal">EXEC SQL elif <em class="replaceable"><code>name</code></em>;</code></span> <a href="#ECPG-IFDEF-ELIF" class="id_link">#</a></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 id="ECPG-IFDEF-ELSE"><span class="term"><code class="literal">EXEC SQL else;</code></span> <a href="#ECPG-IFDEF-ELSE" class="id_link">#</a></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 id="ECPG-IFDEF-ENDIF"><span class="term"><code class="literal">EXEC SQL endif;</code></span> <a href="#ECPG-IFDEF-ENDIF" class="id_link">#</a></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. Processing Embedded SQL Programs">Next</a></td></tr><tr><td width="40%" align="left" valign="top">36.8. Error Handling </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 36.10. Processing Embedded SQL Programs</td></tr></table></div></body></html>
+\ No newline at end of file
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-04-13 13:44:03 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-04-13 13:44:03 +0000
commit	293913568e6a7a86fd1479e1cff8e2ecb58d6568 (patch)
tree	fc3b469a3ec5ab71b36ea97cc7aaddb838423a0c /doc/src/sgml/html/ecpg-preproc.html
parent	Initial commit. (diff)
download	postgresql-16-293913568e6a7a86fd1479e1cff8e2ecb58d6568.tar.xz postgresql-16-293913568e6a7a86fd1479e1cff8e2ecb58d6568.zip