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<h2 class="title" style="clear: both"><a id="dbset_re_source"></a>Db::set_re_source()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
Db::set_re_source(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 either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp5840200"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp5838784"></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="idp5849168"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">Db::set_re_source()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or 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="idp5865800"></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="idp5867128"></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="idp5851344"></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>
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