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<h2 class="title" style="clear: both"><a id="dbset_dup_compare"></a>DB->set_dup_compare()</h2>
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<pre class="programlisting">#include <db.h>
int
DB->set_dup_compare(DB *db,
int (*dup_compare_fcn)(DB *db, const DBT *dbt, const DBT *dbt2)); </pre>
<p>
Set the duplicate data item comparison function. The comparison
function is called whenever it is necessary to compare a data item
specified by the application with a data item currently stored in the
database. Calling <code class="methodname">DB->set_dup_compare()</code> implies calling
<a class="xref" href="dbset_flags.html" title="DB->set_flags()">DB->set_flags()</a> with the
<a class="link" href="dbset_flags.html#dbset_flags_DB_DUPSORT">DB_DUPSORT</a>
flag.
</p>
<p>
If no comparison function is specified, the data items are compared
lexically, with shorter data items collating before longer data items.
</p>
<p>
The <code class="methodname">DB->set_dup_compare()</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_dup_compare()</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_dup_compare()</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="id1644205"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1644821"></a>dup_compare_fcn</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>dup_compare_fcn</strong></span> function is the
application-specified duplicate data item comparison function. The
function takes three arguments:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">db</code>
</p>
<p>
The <span class="bold"><strong>db</strong></span> parameter is the enclosing
database handle.
</p>
</li>
<li>
<p>
<code class="literal">dbt1</code>
</p>
<p>
The <span class="bold"><strong>dbt1</strong></span> parameter is a
<a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the application
supplied data item.
</p>
</li>
<li>
<p>
<code class="literal">dbt2</code>
</p>
<p>
The <span class="bold"><strong>dbt2</strong></span> parameter is a
<a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> representing the current
tree's data item.
</p>
</li>
</ul>
</div>
<p>
The <span class="bold"><strong>dup_compare_fcn</strong></span> function must return an
integer value less than, equal to, or greater than zero if the first data item
parameter is considered to be respectively less than, equal to, or greater than
the second data item parameter. In addition, the comparison function must cause
the data items in the set to be <span class="emphasis"><em>well-ordered</em></span>. The
comparison function must correctly handle any data item values used by the
application (possibly including zero-length data items). The
<span class="bold"><strong>data</strong></span> and <span class="bold"><strong>size</strong></span>
fields of the <a class="link" href="dbt.html" title="Chapter 4. The DBT Handle">DBT</a> are the only fields
that may be used for the purposes of this comparison, and no particular
alignment of the memory to which the <span class="bold"><strong>data</strong></span> field
refers may be assumed.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1645149"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB->set_dup_compare()</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="id1645022"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
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="id1645023"></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="id1645125"></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>
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