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124 lines
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124 lines
5.7 KiB
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<title>fseek (The Red Hat newlib C Library)</title>
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<link href="_005f_005ffsetlocking.html#g_t_005f_005ffsetlocking" rel="next" title="__fsetlocking">
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<a name="fseek"></a>
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<div class="header">
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<p>
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Next: <a href="_005f_005ffsetlocking.html#g_t_005f_005ffsetlocking" accesskey="n" rel="next">__fsetlocking</a>, Previous: <a href="freopen.html#freopen" accesskey="p" rel="prev">freopen</a>, Up: <a href="Stdio.html#Stdio" accesskey="u" rel="up">Stdio</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="fseek_002c-fseeko_002d_002d_002dset-file-position"></a>
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<h3 class="section">4.26 <code>fseek</code>, <code>fseeko</code>—set file position</h3>
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<a name="index-fseek"></a>
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<a name="index-fseeko"></a>
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<a name="index-_005ffseek_005fr"></a>
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<a name="index-_005ffseeko_005fr"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <stdio.h>
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int fseek(FILE *<var>fp</var>, long <var>offset</var>, int <var>whence</var>);
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int fseeko(FILE *<var>fp</var>, off_t <var>offset</var>, int <var>whence</var>);
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int _fseek_r(struct _reent *<var>ptr</var>, FILE *<var>fp</var>,
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long <var>offset</var>, int <var>whence</var>);
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int _fseeko_r(struct _reent *<var>ptr</var>, FILE *<var>fp</var>,
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off_t <var>offset</var>, int <var>whence</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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Objects of type <code>FILE</code> can have a “position” that records how much
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of the file your program has already read. Many of the <code>stdio</code> functions
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depend on this position, and many change it as a side effect.
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</p>
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<p>You can use <code>fseek</code>/<code>fseeko</code> to set the position for the file identified by
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<var>fp</var>. The value of <var>offset</var> determines the new position, in one
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of three ways selected by the value of <var>whence</var> (defined as macros
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in ‘<code>stdio.h</code>’):
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</p>
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<p><code>SEEK_SET</code>—<var>offset</var> is the absolute file position (an offset
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from the beginning of the file) desired. <var>offset</var> must be positive.
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</p>
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<p><code>SEEK_CUR</code>—<var>offset</var> is relative to the current file position.
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<var>offset</var> can meaningfully be either positive or negative.
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</p>
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<p><code>SEEK_END</code>—<var>offset</var> is relative to the current end of file.
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<var>offset</var> can meaningfully be either positive (to increase the size
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of the file) or negative.
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</p>
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<p>See <code>ftell</code>/<code>ftello</code> to determine the current file position.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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<code>fseek</code>/<code>fseeko</code> return <code>0</code> when successful. On failure, the
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result is <code>EOF</code>. The reason for failure is indicated in <code>errno</code>:
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either <code>ESPIPE</code> (the stream identified by <var>fp</var> doesn’t support
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repositioning) or <code>EINVAL</code> (invalid file position).
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</p>
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<br>
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<p><strong>Portability</strong><br>
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ANSI C requires <code>fseek</code>.
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</p>
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<p><code>fseeko</code> is defined by the Single Unix specification.
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</p>
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<p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>,
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<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
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</p>
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<br>
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<hr>
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<div class="header">
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<p>
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Next: <a href="_005f_005ffsetlocking.html#g_t_005f_005ffsetlocking" accesskey="n" rel="next">__fsetlocking</a>, Previous: <a href="freopen.html#freopen" accesskey="p" rel="prev">freopen</a>, Up: <a href="Stdio.html#Stdio" accesskey="u" rel="up">Stdio</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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