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143 lines
6.7 KiB
HTML
143 lines
6.7 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>funopen (The Red Hat newlib C Library)</title>
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<meta name="description" content="funopen (The Red Hat newlib C Library)">
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<meta name="keywords" content="funopen (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="funopen"></a>
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<div class="header">
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<p>
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Next: <a href="fwide.html#fwide" accesskey="n" rel="next">fwide</a>, Previous: <a href="ftell.html#ftell" accesskey="p" rel="prev">ftell</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="funopen_002c-fropen_002c-fwopen_002d_002d_002dopen-a-stream-with-custom-callbacks"></a>
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<h3 class="section">4.30 <code>funopen</code>, <code>fropen</code>, <code>fwopen</code>—open a stream with custom callbacks</h3>
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<a name="index-funopen"></a>
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<a name="index-fropen"></a>
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<a name="index-fwopen"></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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FILE *funopen(const void *<var>cookie</var>,
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int (*<var>readfn</var>) (void *cookie, char *buf, int n),
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int (*<var>writefn</var>) (void *cookie, const char *buf, int n),
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fpos_t (*<var>seekfn</var>) (void *cookie, fpos_t off, int whence),
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int (*<var>closefn</var>) (void *cookie));
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FILE *fropen(const void *<var>cookie</var>,
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int (*<var>readfn</var>) (void *cookie, char *buf, int n));
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FILE *fwopen(const void *<var>cookie</var>,
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int (*<var>writefn</var>) (void *cookie, const char *buf, int n));
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</pre></div>
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<p><strong>Description</strong><br>
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<code>funopen</code> creates a <code>FILE</code> stream where I/O is performed using
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custom callbacks. At least one of <var>readfn</var> and <var>writefn</var> must be
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provided, which determines whether the stream behaves with mode <"r">,
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<"w">, or <"r+">.
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</p>
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<p><var>readfn</var> should return -1 on failure, or else the number of bytes
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read (0 on EOF). It is similar to <code>read</code>, except that <int> rather
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than <size_t> bounds a transaction size, and <var>cookie</var> will be passed
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as the first argument. A NULL <var>readfn</var> makes attempts to read the
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stream fail.
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</p>
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<p><var>writefn</var> should return -1 on failure, or else the number of bytes
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written. It is similar to <code>write</code>, except that <int> rather than
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<size_t> bounds a transaction size, and <var>cookie</var> will be passed as
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the first argument. A NULL <var>writefn</var> makes attempts to write the
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stream fail.
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</p>
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<p><var>seekfn</var> should return (fpos_t)-1 on failure, or else the current
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file position. It is similar to <code>lseek</code>, except that <var>cookie</var>
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will be passed as the first argument. A NULL <var>seekfn</var> makes the
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stream behave similarly to a pipe in relation to stdio functions that
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require positioning. This implementation assumes fpos_t and off_t are
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the same type.
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</p>
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<p><var>closefn</var> should return -1 on failure, or 0 on success. It is
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similar to <code>close</code>, except that <var>cookie</var> will be passed as the
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first argument. A NULL <var>closefn</var> merely flushes all data then lets
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<code>fclose</code> succeed. A failed close will still invalidate the stream.
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</p>
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<p>Read and write I/O functions are allowed to change the underlying
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buffer on fully buffered or line buffered streams by calling
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<code>setvbuf</code>. They are also not required to completely fill or empty
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the buffer. They are not, however, allowed to change streams from
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unbuffered to buffered or to change the state of the line buffering
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flag. They must also be prepared to have read or write calls occur on
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buffers other than the one most recently specified.
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</p>
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<p>The functions <code>fropen</code> and <code>fwopen</code> are convenience macros around
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<code>funopen</code> that only use the specified callback.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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The return value is an open FILE pointer on success. On error,
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<code>NULL</code> is returned, and <code>errno</code> will be set to EINVAL if a
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function pointer is missing, ENOMEM if the stream cannot be created,
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or EMFILE if too many streams are already open.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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This function is a newlib extension, copying the prototype from BSD.
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It is not portable. See also the <code>fopencookie</code> interface from Linux.
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</p>
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<p>Supporting OS subroutines required: <code>sbrk</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="fwide.html#fwide" accesskey="n" rel="next">fwide</a>, Previous: <a href="ftell.html#ftell" accesskey="p" rel="prev">ftell</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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</body>
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</html>
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