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113 lines
4.8 KiB
HTML
113 lines
4.8 KiB
HTML
4 years ago
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<title>ftell (The Red Hat newlib C Library)</title>
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<meta name="description" content="ftell (The Red Hat newlib C Library)">
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Stdio.html#Stdio" rel="up" title="Stdio">
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<link href="funopen.html#funopen" rel="next" title="funopen">
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</head>
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<body lang="en">
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<a name="ftell"></a>
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<div class="header">
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<p>
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Next: <a href="funopen.html#funopen" accesskey="n" rel="next">funopen</a>, Previous: <a href="fsetpos.html#fsetpos" accesskey="p" rel="prev">fsetpos</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="ftell_002c-ftello_002d_002d_002dreturn-position-in-a-stream-or-file"></a>
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<h3 class="section">4.29 <code>ftell</code>, <code>ftello</code>—return position in a stream or file</h3>
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<a name="index-ftell"></a>
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<a name="index-ftello"></a>
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<a name="index-_005fftell_005fr"></a>
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<a name="index-_005fftello_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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long ftell(FILE *<var>fp</var>);
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off_t ftello(FILE *<var>fp</var>);
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long _ftell_r(struct _reent *<var>ptr</var>, FILE *<var>fp</var>);
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off_t _ftello_r(struct _reent *<var>ptr</var>, FILE *<var>fp</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>The result of <code>ftell</code>/<code>ftello</code> is the current position for a file
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identified by <var>fp</var>. If you record this result, you can later
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use it with <code>fseek</code>/<code>fseeko</code> to return the file to this
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position. The difference between <code>ftell</code> and <code>ftello</code> is that
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<code>ftell</code> returns <code>long</code> and <code>ftello</code> returns <code>off_t</code>.
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</p>
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<p>In the current implementation, <code>ftell</code>/<code>ftello</code> simply uses a character
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count to represent the file position; this is the same number that
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would be recorded by <code>fgetpos</code>.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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<code>ftell</code>/<code>ftello</code> return the file position, if possible. If they cannot do
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this, they return <code>-1L</code>. Failure occurs on streams that do not support
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positioning; the global <code>errno</code> indicates this condition with the
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value <code>ESPIPE</code>.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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<code>ftell</code> is required by the ANSI C standard, but the meaning of its
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result (when successful) is not specified beyond requiring that it be
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acceptable as an argument to <code>fseek</code>. In particular, other
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conforming C implementations may return a different result from
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<code>ftell</code> than what <code>fgetpos</code> records.
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</p>
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<p><code>ftello</code> is defined by the Single Unix specification.
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</p>
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<p>No supporting OS subroutines are required.
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</p>
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<br>
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</body>
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