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104 lines
4.1 KiB
HTML
104 lines
4.1 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<title>fileno (The Red Hat newlib C Library)</title>
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<meta name="description" content="fileno (The Red Hat newlib C Library)">
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<meta name="keywords" content="fileno (The Red Hat newlib C Library)">
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<link href="index.html#Top" rel="start" title="Top">
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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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</head>
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<body lang="en">
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<a name="fileno"></a>
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<div class="header">
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<p>
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Next: <a href="fmemopen.html#fmemopen" accesskey="n" rel="next">fmemopen</a>, Previous: <a href="fgetws.html#fgetws" accesskey="p" rel="prev">fgetws</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="fileno_002c-fileno_005funlocked_002d_002d_002dreturn-file-descriptor-associated-with-stream"></a>
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<h3 class="section">4.15 <code>fileno</code>, <code>fileno_unlocked</code>—return file descriptor associated with stream</h3>
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<a name="index-fileno"></a>
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<a name="index-fileno_005funlocked"></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 fileno(FILE *<var>fp</var>);
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#define _BSD_SOURCE
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#include <stdio.h>
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int fileno_unlocked(FILE *<var>fp</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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You can use <code>fileno</code> to return the file descriptor identified by <var>fp</var>.
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</p>
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<p><code>fileno_unlocked</code> is a non-thread-safe version of <code>fileno</code>.
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<code>fileno_unlocked</code> may only safely be used within a scope
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protected by flockfile() (or ftrylockfile()) and funlockfile(). This
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function may safely be used in a multi-threaded program if and only
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if they are called while the invoking thread owns the (FILE *)
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object, as is the case after a successful call to the flockfile() or
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ftrylockfile() functions. If threads are disabled, then
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<code>fileno_unlocked</code> is equivalent to <code>fileno</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>fileno</code> returns a non-negative integer when successful.
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If <var>fp</var> is not an open stream, <code>fileno</code> returns -1.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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<code>fileno</code> is not part of ANSI C.
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POSIX requires <code>fileno</code>.
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</p>
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<p><code>fileno_unlocked</code> is a BSD extension also provided by GNU libc.
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</p>
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<p>Supporting OS subroutines required: none.
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</p>
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<br>
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</body>
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</html>
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