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<title>Vorbisfile - function - ov_test_callbacks</title>
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<td><p class=tiny>Vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td>
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<h1>ov_test_callbacks</h1>

<p><i>declared in "vorbis/vorbisfile.h";</i></p>

<p>This is an alternative function used to open and test an OggVorbis_File
structure when using a data source other than a file,
when its necessary to modify default file access behavior, or to
test for Vorbis content from a <tt>FILE *</tt> pointer under
Windows where <a href="ov_open.html">ov_test()</a> cannot be used.  It
allows the application to specify custom file manipulation routines
and sets up all the related decoding structures.

<p>Once this has been called, the same <tt>OggVorbis_File</tt>
struct should be passed to all the libvorbisfile functions.
<p>
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<pre><b>
int ov_test_callbacks(void *datasource, <a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *initial, long ibytes, <a href="ov_callbacks.html">ov_callbacks</a> callbacks);
</b></pre>
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<h3>Parameters</h3>
<dl>
<dt><i>f</i></dt>
<dd>File pointer to an already opened file
or pipe (it need not be seekable--though this obviously restricts what
can be done with the bitstream).</dd>
<dt><i>vf</i></dt>
<dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
functions. Once this has been called, the same <tt>OggVorbis_File</tt>
struct should be passed to all the libvorbisfile functions.</dd>
<dt><i>initial</i></dt>
<dd>Typically set to NULL.  This parameter is useful if some data has already been
read from the file and the stream is not seekable. It is used in conjunction with <tt>ibytes</tt>.  In this case, <tt>initial</tt>
should be a pointer to a buffer containing the data read.</dd>
<dt><i>ibytes</i></dt>
<dd>Typically set to 0.  This parameter is useful if some data has already been
read from the file and the stream is not seekable. In this case, <tt>ibytes</tt>
should contain the length (in bytes) of the buffer.  Used together with <tt>initial</tt>.</dd>
<dt><i>callbacks</i></dt>
<dd>A completed <a href="ov_callbacks.html">ov_callbacks</a> struct which indicates desired custom file manipulation routines.  vorbisfile.h defines several preprovided callback sets; see <a href="ov_callbacks.html">ov_callbacks</a> for details.</dd>
</dl>


<h3>Return Values</h3>
<blockquote>
<li>0 for success</li>
<li>less than zero for failure:</li>
<ul>
<li>OV_EREAD - A read from media returned an error.</li>
<li>OV_ENOTVORBIS - Bitstream contains no Vorbis data.</li>
<li>OV_EVERSION - Vorbis version mismatch.</li>
<li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
<li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
</ul>
</blockquote>
<p>

<h3>Notes</h3>
<dl>

<dt><b>[a] Windows and use as an ov_test() substitute</b><p> Windows
applications should not use <a href="ov_test.html">ov_test()</a> due
to the likelihood of <a href="ov_open.html#winfoot">CRT linking
mismatches and runtime protection faults
[ov_open:a]</a>. ov_test_callbacks() is a safe substitute; specifically:

<pre><tt>ov_test_callbacks(f, vf, initial, ibytes, OV_CALLBACKS_DEFAULT);</tt>
</pre>

... provides exactly the same functionality as <a
href="ov_test.html">ov_test()</a> but will always work correctly under
Windows, regardless of linking setup details.<p>

</dl>

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<td><p class=tiny>copyright &copy; 2007 Xiph.org</p></td>
<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
</tr><tr>
<td><p class=tiny>Vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td>
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