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149 lines
6.5 KiB
HTML
149 lines
6.5 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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<html>
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>fopencookie (The Red Hat newlib C Library)</title>
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<meta name="description" content="fopencookie (The Red Hat newlib C Library)">
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<meta name="keywords" content="fopencookie (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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</head>
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<body lang="en">
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<a name="fopencookie"></a>
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<div class="header">
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<p>
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Next: <a href="fpurge.html#fpurge" accesskey="n" rel="next">fpurge</a>, Previous: <a href="fopen.html#fopen" accesskey="p" rel="prev">fopen</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="fopencookie_002d_002d_002dopen-a-stream-with-custom-callbacks"></a>
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<h3 class="section">4.18 <code>fopencookie</code>—open a stream with custom callbacks</h3>
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<a name="index-fopencookie"></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 *fopencookie(const void *<var>cookie</var>, const char *<var>mode</var>,
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cookie_io_functions_t <var>functions</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>fopencookie</code> creates a <code>FILE</code> stream where I/O is performed using
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custom callbacks. The callbacks are registered via the structure:
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</p>
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<p>typedef ssize_t (*cookie_read_function_t)(void *_cookie, char *_buf,
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size_t _n);
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typedef ssize_t (*cookie_write_function_t)(void *_cookie,
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const char *_buf, size_t _n);
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typedef int (*cookie_seek_function_t)(void *_cookie, off_t *_off,
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int _whence);
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typedef int (*cookie_close_function_t)(void *_cookie);
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</p>
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<div class="smallexample">
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<pre class="smallexample"> typedef struct
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{
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cookie_read_function_t *read;
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cookie_write_function_t *write;
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cookie_seek_function_t *seek;
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cookie_close_function_t *close;
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} cookie_io_functions_t;
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</pre></div>
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<p>The stream is opened with <var>mode</var> treated as in <code>fopen</code>. The
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callbacks <var>functions.read</var> and <var>functions.write</var> may only be NULL
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when <var>mode</var> does not require them.
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</p>
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<p><var>functions.read</var> should return -1 on failure, or else the number of
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bytes read (0 on EOF). It is similar to <code>read</code>, except that
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<var>cookie</var> will be passed as the first argument.
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</p>
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<p><var>functions.write</var> should return -1 on failure, or else the number of
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bytes written. It is similar to <code>write</code>, except that <var>cookie</var>
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will be passed as the first argument.
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</p>
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<p><var>functions.seek</var> should return -1 on failure, and 0 on success, with
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<var>_off</var> set to the current file position. It is a cross between
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<code>lseek</code> and <code>fseek</code>, with the <var>_whence</var> argument interpreted in
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the same manner. A NULL <var>functions.seek</var> makes the stream behave
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similarly to a pipe in relation to stdio functions that require
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positioning.
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</p>
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<p><var>functions.close</var> should return -1 on failure, or 0 on success. It
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is similar to <code>close</code>, except that <var>cookie</var> will be passed as the
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first argument. A NULL <var>functions.close</var> merely flushes all data
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then lets <code>fclose</code> succeed. A failed close will still invalidate
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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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<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 or <var>mode</var> is invalid, ENOMEM if the
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stream cannot be created, or EMFILE if too many streams are already
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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 Linux.
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It is not portable. See also the <code>funopen</code> interface from BSD.
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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="fpurge.html#fpurge" accesskey="n" rel="next">fpurge</a>, Previous: <a href="fopen.html#fopen" accesskey="p" rel="prev">fopen</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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