<?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>Chapter 34. libpq - C Library</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="client-interfaces.html" title="Part IV. Client Interfaces" /><link rel="next" href="libpq-connect.html" title="34.1. Database Connection Control Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">Chapter 34. <span xmlns="http://www.w3.org/1999/xhtml" class="application">libpq</span> - C Library</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="client-interfaces.html" title="Part IV. Client Interfaces">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="client-interfaces.html" title="Part IV. Client Interfaces">Up</a></td><th width="60%" align="center">Part IV. Client Interfaces</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-connect.html" title="34.1. Database Connection Control Functions">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="LIBPQ"><div class="titlepage"><div><div><h2 class="title">Chapter 34. <span class="application">libpq</span> - C Library</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="libpq-connect.html">34.1. Database Connection Control Functions</a></span></dt><dd><dl><dt><span class="sect2"><a href="libpq-connect.html#LIBPQ-CONNSTRING">34.1.1. Connection Strings</a></span></dt><dt><span class="sect2"><a href="libpq-connect.html#LIBPQ-PARAMKEYWORDS">34.1.2. Parameter Key Words</a></span></dt></dl></dd><dt><span class="sect1"><a href="libpq-status.html">34.2. Connection Status Functions</a></span></dt><dt><span class="sect1"><a href="libpq-exec.html">34.3. Command Execution Functions</a></span></dt><dd><dl><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-MAIN">34.3.1. Main Functions</a></span></dt><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-SELECT-INFO">34.3.2. Retrieving Query Result Information</a></span></dt><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-NONSELECT">34.3.3. Retrieving Other Result Information</a></span></dt><dt><span class="sect2"><a href="libpq-exec.html#LIBPQ-EXEC-ESCAPE-STRING">34.3.4. Escaping Strings for Inclusion in SQL Commands</a></span></dt></dl></dd><dt><span class="sect1"><a href="libpq-async.html">34.4. Asynchronous Command Processing</a></span></dt><dt><span class="sect1"><a href="libpq-single-row-mode.html">34.5. Retrieving Query Results Row-By-Row</a></span></dt><dt><span class="sect1"><a href="libpq-cancel.html">34.6. Canceling Queries in Progress</a></span></dt><dt><span class="sect1"><a href="libpq-fastpath.html">34.7. The Fast-Path Interface</a></span></dt><dt><span class="sect1"><a href="libpq-notify.html">34.8. Asynchronous Notification</a></span></dt><dt><span class="sect1"><a href="libpq-copy.html">34.9. Functions Associated with the <code class="command">COPY</code> Command</a></span></dt><dd><dl><dt><span class="sect2"><a href="libpq-copy.html#LIBPQ-COPY-SEND">34.9.1. Functions for Sending <code class="command">COPY</code> Data</a></span></dt><dt><span class="sect2"><a href="libpq-copy.html#LIBPQ-COPY-RECEIVE">34.9.2. Functions for Receiving <code class="command">COPY</code> Data</a></span></dt><dt><span class="sect2"><a href="libpq-copy.html#LIBPQ-COPY-DEPRECATED">34.9.3. Obsolete Functions for <code class="command">COPY</code></a></span></dt></dl></dd><dt><span class="sect1"><a href="libpq-control.html">34.10. Control Functions</a></span></dt><dt><span class="sect1"><a href="libpq-misc.html">34.11. Miscellaneous Functions</a></span></dt><dt><span class="sect1"><a href="libpq-notice-processing.html">34.12. Notice Processing</a></span></dt><dt><span class="sect1"><a href="libpq-events.html">34.13. Event System</a></span></dt><dd><dl><dt><span class="sect2"><a href="libpq-events.html#LIBPQ-EVENTS-TYPES">34.13.1. Event Types</a></span></dt><dt><span class="sect2"><a href="libpq-events.html#LIBPQ-EVENTS-PROC">34.13.2. Event Callback Procedure</a></span></dt><dt><span class="sect2"><a href="libpq-events.html#LIBPQ-EVENTS-FUNCS">34.13.3. Event Support Functions</a></span></dt><dt><span class="sect2"><a href="libpq-events.html#LIBPQ-EVENTS-EXAMPLE">34.13.4. Event Example</a></span></dt></dl></dd><dt><span class="sect1"><a href="libpq-envars.html">34.14. Environment Variables</a></span></dt><dt><span class="sect1"><a href="libpq-pgpass.html">34.15. The Password File</a></span></dt><dt><span class="sect1"><a href="libpq-pgservice.html">34.16. The Connection Service File</a></span></dt><dt><span class="sect1"><a href="libpq-ldap.html">34.17. LDAP Lookup of Connection Parameters</a></span></dt><dt><span class="sect1"><a href="libpq-ssl.html">34.18. SSL Support</a></span></dt><dd><dl><dt><span class="sect2"><a href="libpq-ssl.html#LIBQ-SSL-CERTIFICATES">34.18.1. Client Verification of Server Certificates</a></span></dt><dt><span class="sect2"><a href="libpq-ssl.html#LIBPQ-SSL-CLIENTCERT">34.18.2. Client Certificates</a></span></dt><dt><span class="sect2"><a href="libpq-ssl.html#LIBPQ-SSL-PROTECTION">34.18.3. Protection Provided in Different Modes</a></span></dt><dt><span class="sect2"><a href="libpq-ssl.html#LIBPQ-SSL-FILEUSAGE">34.18.4. SSL Client File Usage</a></span></dt><dt><span class="sect2"><a href="libpq-ssl.html#LIBPQ-SSL-INITIALIZE">34.18.5. SSL Library Initialization</a></span></dt></dl></dd><dt><span class="sect1"><a href="libpq-threading.html">34.19. Behavior in Threaded Programs</a></span></dt><dt><span class="sect1"><a href="libpq-build.html">34.20. Building <span class="application">libpq</span> Programs</a></span></dt><dt><span class="sect1"><a href="libpq-example.html">34.21. Example Programs</a></span></dt></dl></div><a id="id-1.7.3.2" class="indexterm"></a><a id="id-1.7.3.3" class="indexterm"></a><p> <span class="application">libpq</span> is the <acronym class="acronym">C</acronym> application programmer's interface to <span class="productname">PostgreSQL</span>. <span class="application">libpq</span> is a set of library functions that allow client programs to pass queries to the <span class="productname">PostgreSQL</span> backend server and to receive the results of these queries. </p><p> <span class="application">libpq</span> is also the underlying engine for several other <span class="productname">PostgreSQL</span> application interfaces, including those written for C++, Perl, Python, Tcl and <span class="application">ECPG</span>. So some aspects of <span class="application">libpq</span>'s behavior will be important to you if you use one of those packages. In particular, <a class="xref" href="libpq-envars.html" title="34.14. Environment Variables">Section 34.14</a>, <a class="xref" href="libpq-pgpass.html" title="34.15. The Password File">Section 34.15</a> and <a class="xref" href="libpq-ssl.html" title="34.18. SSL Support">Section 34.18</a> describe behavior that is visible to the user of any application that uses <span class="application">libpq</span>. </p><p> Some short programs are included at the end of this chapter (<a class="xref" href="libpq-example.html" title="34.21. Example Programs">Section 34.21</a>) to show how to write programs that use <span class="application">libpq</span>. There are also several complete examples of <span class="application">libpq</span> applications in the directory <code class="filename">src/test/examples</code> in the source code distribution. </p><p> Client programs that use <span class="application">libpq</span> must include the header file <code class="filename">libpq-fe.h</code><a id="id-1.7.3.7.3" class="indexterm"></a> and must link with the <span class="application">libpq</span> library. </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="client-interfaces.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="client-interfaces.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="libpq-connect.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part IV. 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