<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Loading libdbi at runtime</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="Database Independent Abstraction Layer for C" HREF="index.html"><LINK REL="UP" TITLE="libdbi in a Nutshell (Quickstart Guide)" HREF="quickstart.html"><LINK REL="PREVIOUS" TITLE="Generic Example Program" HREF="quickstart-code.html"><LINK REL="NEXT" TITLE="Adding libdbi to your project" HREF="x276.html"></HEAD ><BODY CLASS="SECTION" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Database Independent Abstraction Layer for C: libdbi Programmer's Guide</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="quickstart-code.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 2. libdbi in a Nutshell (Quickstart Guide)</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x276.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECTION" ><H1 CLASS="SECTION" ><A NAME="AEN267" >2.3. Loading libdbi at runtime</A ></H1 ><P >The generic example shown in the previous section assumed that the program is linked against libdbi. This is in fact the recommended way to add libdbi functionality to your programs. However, there are situations where this approach will not work. Some programs are designed to load modules at runtime to extend their capabilities. A well-known example is the web server Apache, which uses loadable modules to custom-tailor its capabilities. If such a module were to use libdbi, we'd look at the following pattern:</P ><DIV CLASS="INFORMALEXAMPLE" ><P ></P ><A NAME="AEN270" ></A ><P >Parent => dl_open(module) => dl_open(driver)</P ><P ></P ></DIV ><P >The dynamically loaded module is linked against libdbi whereas the parent application is not. For this pattern to work, the drivers are linked against libdbi by default. This avoids "undefined symbol" errors at runtime, but may cause problems under arcane conditions or on equally arcane operating systems. If you should ever encounter such problems, you can switch off linking the drivers against libdbi like this:</P ><TABLE BORDER="0" BGCOLOR="#000000" WIDTH="100%" ><TR ><TD ><FONT COLOR="#32CD32" ><PRE CLASS="SCREEN" ><SAMP CLASS="PROMPT" >~/libdbi-drivers #</SAMP ><KBD CLASS="USERINPUT" >./configure --disable-libdbi --with-mysql</KBD ></PRE ></FONT ></TD ></TR ></TABLE ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="quickstart-code.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="x276.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Generic Example Program</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="quickstart.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Adding libdbi to your project</TD ></TR ></TABLE ></DIV ></BODY ></HTML >