<?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>DB->set_re_source()</title> <link rel="stylesheet" href="apiReference.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> <link rel="start" href="index.html" title="Berkeley DB C API Reference" /> <link rel="up" href="db.html" title="Chapter 2. The DB Handle" /> <link rel="prev" href="dbset_re_pad.html" title="DB->set_re_pad()" /> <link rel="next" href="dbstat.html" title="DB->stat()" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DB->set_re_source()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="dbset_re_pad.html">Prev</a> </td> <th width="60%" align="center">Chapter 2. The DB Handle </th> <td width="20%" align="right"> <a accesskey="n" href="dbstat.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="dbset_re_source"></a>DB->set_re_source()</h2> </div> </div> </div> <pre class="programlisting">#include <db.h> int DB->set_re_source(DB *db, char *source); </pre> <p> Set the underlying source file for the Recno access method. The purpose of the <span class="bold"><strong>source</strong></span> value is to provide fast access and modification to databases that are normally stored as flat text files. </p> <p> The <span class="bold"><strong>source</strong></span> parameter specifies an underlying flat text database file that is read to initialize a transient record number index. In the case of variable length records, the records are separated, as specified by <a class="xref" href="dbset_re_delim.html" title="DB->set_re_delim()">DB->set_re_delim()</a>. For example, standard UNIX byte stream files can be interpreted as a sequence of variable length records separated by <newline> characters. </p> <p> In addition, when cached data would normally be written back to the underlying database file (for example, the <a class="xref" href="dbclose.html" title="DB->close()">DB->close()</a> or <a class="xref" href="dbsync.html" title="DB->sync()">DB->sync()</a> methods are called), the in-memory copy of the database will be written back to the <span class="bold"><strong>source</strong></span> file. </p> <p> By default, the backing source file is read lazily; that is, records are not read from the file until they are requested by the application. <span class="bold"><strong>If multiple processes (not threads) are accessing a Recno database concurrently, and are either inserting or deleting records, the backing source file must be read in its entirety before more than a single process accesses the database, and only that process should specify the backing source file as part of the <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> call. See the <a class="link" href="dbset_flags.html#dbset_flags_DB_SNAPSHOT">DB_SNAPSHOT</a> flag for more information.</strong></span> </p> <p> <span class="bold"><strong>Reading and writing the backing source file specified by <span class="bold"><strong>source</strong></span> cannot be transaction-protected because it involves filesystem operations that are not part of the Db transaction methodology.</strong></span> For this reason, if a temporary database is used to hold the records, it is possible to lose the contents of the <span class="bold"><strong>source</strong></span> file, for example, if the system crashes at the right instant. If a file is used to hold the database, normal database recovery on that file can be used to prevent information loss, although it is still possible that the contents of <span class="bold"><strong>source</strong></span> will be lost if the system crashes. </p> <p> The <span class="bold"><strong>source</strong></span> file must already exist (but may be zero-length) when <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> is called. </p> <p> It is not an error to specify a read-only <span class="bold"><strong>source</strong></span> file when creating a database, nor is it an error to modify the resulting database. However, any attempt to write the changes to the backing source file using either the <a class="xref" href="dbsync.html" title="DB->sync()">DB->sync()</a> or <a class="xref" href="dbclose.html" title="DB->close()">DB->close()</a> methods will fail, of course. Specify the <a class="link" href="dbclose.html#dbclose_DB_NOSYNC">DB_NOSYNC</a> flag to the <a class="xref" href="dbclose.html" title="DB->close()">DB->close()</a> method to stop it from attempting to write the changes to the backing file; instead, they will be silently discarded. </p> <p> For all of the previous reasons, the <span class="bold"><strong>source</strong></span> field is generally used to specify databases that are read-only for Berkeley DB applications; and that are either generated on the fly by software tools or modified using a different mechanism — for example, a text editor. </p> <p> The <code class="methodname">DB->set_re_source()</code> method configures operations performed using the specified <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> handle, not all operations performed on the underlying database. </p> <p> The <code class="methodname">DB->set_re_source()</code> method may not be called after the <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method is called. If the database already exists when <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> is called, the information specified to <code class="methodname">DB->set_re_source()</code> must be the same as that historically used to create the database or corruption can occur. </p> <p> The <code class="methodname">DB->set_re_source()</code> <span> <span> method returns a non-zero error value on failure and 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1650586"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1650591"></a>source</h4> </div> </div> </div> <p> The backing flat text database file for a Recno database. </p> <p> When using a Unicode build on Windows (the default), the <span class="bold"><strong>source</strong></span> argument will be interpreted as a UTF-8 string, which is equivalent to ASCII for Latin characters. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1650744"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DB->set_re_source()</code> <span> <span> method may fail and return one of the following non-zero errors: </span> </span> </p> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="id1650760"></a>EINVAL</h4> </div> </div> </div> <p> If the method was called after <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> was called; or if an invalid flag value or parameter was specified. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1650761"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="id1650576"></a>See Also</h3> </div> </div> </div> <p> <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> </p> </div> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="dbset_re_pad.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="db.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="dbstat.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">DB->set_re_pad() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DB->stat()</td> </tr> </table> </div> </body> </html>