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125 lines
5.8 KiB
HTML
125 lines
5.8 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>open_memstream (The Red Hat newlib C Library)</title>
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<meta name="description" content="open_memstream (The Red Hat newlib C Library)">
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<meta name="keywords" content="open_memstream (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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<body lang="en">
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<a name="open_005fmemstream"></a>
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<div class="header">
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<p>
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Next: <a href="perror.html#perror" accesskey="n" rel="next">perror</a>, Previous: <a href="mktemp.html#mktemp" accesskey="p" rel="prev">mktemp</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="open_005fmemstream_002c-open_005fwmemstream_002d_002d_002dopen-a-write-stream-around-an-arbitrary_002dlength-string"></a>
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<h3 class="section">4.43 <code>open_memstream</code>, <code>open_wmemstream</code>—open a write stream around an arbitrary-length string</h3>
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<a name="index-open_005fmemstream"></a>
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<a name="index-open_005fwmemstream"></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 *open_memstream(char **restrict <var>buf</var>,
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size_t *restrict <var>size</var>);
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#include <wchar.h>
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FILE *open_wmemstream(wchar_t **restrict <var>buf</var>,
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size_t *restrict <var>size</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>open_memstream</code> creates a seekable, byte-oriented <code>FILE</code> stream that
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wraps an arbitrary-length buffer, created as if by <code>malloc</code>. The current
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contents of *<var>buf</var> are ignored; this implementation uses *<var>size</var>
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as a hint of the maximum size expected, but does not fail if the hint
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was wrong. The parameters <var>buf</var> and <var>size</var> are later stored
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through following any call to <code>fflush</code> or <code>fclose</code>, set to the
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current address and usable size of the allocated string; although
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after fflush, the pointer is only valid until another stream operation
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that results in a write. Behavior is undefined if the user alters
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either *<var>buf</var> or *<var>size</var> prior to <code>fclose</code>.
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</p>
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<p><code>open_wmemstream</code> is like <code>open_memstream</code> just with the associated
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stream being wide-oriented. The size set in <var>size</var> in subsequent
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operations is the number of wide characters.
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</p>
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<p>The stream is write-only, since the user can directly read *<var>buf</var>
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after a flush; see <code>fmemopen</code> for a way to wrap a string with a
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readable stream. The user is responsible for calling <code>free</code> on
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the final *<var>buf</var> after <code>fclose</code>.
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</p>
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<p>Any time the stream is flushed, a NUL byte is written at the current
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position (but is not counted in the buffer length), so that the string
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is always NUL-terminated after at most *<var>size</var> bytes (or wide characters
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in case of <code>open_wmemstream</code>). However, data previously written beyond
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the current stream offset is not lost, and the NUL value written during a
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flush is restored to its previous value when seeking elsewhere in the string.
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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 <var>buf</var>
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or <var>size</var> is NULL, ENOMEM if memory could not be allocated, or
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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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POSIX.1-2008
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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="perror.html#perror" accesskey="n" rel="next">perror</a>, Previous: <a href="mktemp.html#mktemp" accesskey="p" rel="prev">mktemp</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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