<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Driver Capabilities</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="Driver Infrastructure" HREF="driverinfrastructure.html"><LINK REL="PREVIOUS" TITLE="Driver Infrastructure" HREF="driverinfrastructure.html"><LINK REL="NEXT" TITLE="Database directories" HREF="databasedirectories.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 Driver Author's Guide</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="driverinfrastructure.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 2. Driver Infrastructure</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="databasedirectories.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECTION" ><H1 CLASS="SECTION" ><A NAME="DRIVERCAPS" >2.1. Driver Capabilities</A ></H1 ><P >Driver capabilities are essentially an array of key/value pairs which the drivers set when they're loaded. Both the libdbi framework and programs linked against libdbi can query these capabilities and adjust their behaviour accordingly.</P ><DIV CLASS="SECTION" ><H2 CLASS="SECTION" ><A NAME="SETTINGDRIVERCAPS" >2.1.1. Setting driver capabilities</A ></H2 ><P >The perfect place to set driver capabilities is in the <A HREF="driverfuncs-infrastructure.html#DBD-INITIALIZE" >dbd_initialize</A > function which is called right after the driver is loaded by libdbi. To set capabilities, call the _dbd_register_driver_cap function for each of them:</P ><DIV CLASS="FUNCSYNOPSIS" ><P ></P ><A NAME="AEN73" ></A ><P ><CODE ><CODE CLASS="FUNCDEF" >void <B CLASS="FSFUNC" >_dbd_register_driver_cap</B ></CODE >(dbi_driver_t *<VAR CLASS="PDPARAM" >driver</VAR >, const char *<VAR CLASS="PDPARAM" >capname</VAR >, int <VAR CLASS="PDPARAM" >value</VAR >);</CODE ></P ><P ></P ></DIV ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT >Arguments</DT ><DD ><P ><TT CLASS="LITERAL" >driver</TT >: the driver as passed to <A HREF="driverfuncs-infrastructure.html#DBD-INITIALIZE" >dbd_initialize</A >.</P ><P ><TT CLASS="LITERAL" >capname</TT >: A string containing the name of the capability (i.e. the key).</P ><P ><TT CLASS="LITERAL" >value</TT >: The value of the capability.</P ></DD ></DL ></DIV ></DIV ><DIV CLASS="SECTION" ><H2 CLASS="SECTION" ><A NAME="REQUIREDDRIVERCAPS" >2.1.2. Required driver capabilities</A ></H2 ><P >libdbi currently queries only one driver capability.</P ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT >safe_dlclose</DT ><DD ><P >A nonzero value indicates that the driver can safely be unloaded from memory by calling dlclose(). A value of 0 (zero) indicates that the driver should not be unloaded when libdbi is shut down. Drivers must not be unloaded if they, or any library they are linked against, install exit handlers via atexit() as this would leave dangling pointers, causing segfaults on some platforms.</P ></DD ></DL ></DIV ></DIV ><DIV CLASS="SECTION" ><H2 CLASS="SECTION" ><A NAME="RECOMMENDEDDRIVERCAPS" >2.1.3. Recommended driver capabilities</A ></H2 ><P >Two driver capabilities may be of interest to programs using libdbi and should therefore be published by drivers:</P ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT >transaction_support</DT ><DD ><P >A nonzero value indicates that the database engine supports transactions. Therefore functions to start, commit, or roll back transactions may be safely used.</P ></DD ><DT >savepoint_support</DT ><DD ><P >A nonzero value indicates that the database engine supports savepoints within transactions. Functions to set, release, and roll back to savepoints may be safely used.</P ></DD ></DL ></DIV ></DIV ></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="driverinfrastructure.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="databasedirectories.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Driver Infrastructure</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="driverinfrastructure.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Database directories</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
