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127 lines
6.0 KiB
HTML
127 lines
6.0 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>fmemopen (The Red Hat newlib C Library)</title>
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<meta name="description" content="fmemopen (The Red Hat newlib C Library)">
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<meta name="keywords" content="fmemopen (The Red Hat newlib C Library)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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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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</style>
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</head>
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<body lang="en">
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<a name="fmemopen"></a>
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<div class="header">
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<p>
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Next: <a href="fopen.html#fopen" accesskey="n" rel="next">fopen</a>, Previous: <a href="fileno.html#fileno" accesskey="p" rel="prev">fileno</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="fmemopen_002d_002d_002dopen-a-stream-around-a-fixed_002dlength-string"></a>
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<h3 class="section">4.16 <code>fmemopen</code>—open a stream around a fixed-length string</h3>
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<a name="index-fmemopen"></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 *fmemopen(void *restrict <var>buf</var>, size_t <var>size</var>,
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const char *restrict <var>mode</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>fmemopen</code> creates a seekable <code>FILE</code> stream that wraps a
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fixed-length buffer of <var>size</var> bytes starting at <var>buf</var>. The stream
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is opened with <var>mode</var> treated as in <code>fopen</code>, where append mode
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starts writing at the first NUL byte. If <var>buf</var> is NULL, then
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<var>size</var> bytes are automatically provided as if by <code>malloc</code>, with
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the initial size of 0, and <var>mode</var> must contain <code>+</code> so that data
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can be read after it is written.
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</p>
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<p>The stream maintains a current position, which moves according to
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bytes read or written, and which can be one past the end of the array.
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The stream also maintains a current file size, which is never greater
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than <var>size</var>. If <var>mode</var> starts with <code>r</code>, the position starts at
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<code>0</code>, and file size starts at <var>size</var> if <var>buf</var> was provided. If
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<var>mode</var> starts with <code>w</code>, the position and file size start at <code>0</code>,
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and if <var>buf</var> was provided, the first byte is set to NUL. If
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<var>mode</var> starts with <code>a</code>, the position and file size start at the
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location of the first NUL byte, or else <var>size</var> if <var>buf</var> was
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provided.
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</p>
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<p>When reading, NUL bytes have no significance, and reads cannot exceed
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the current file size. When writing, the file size can increase up to
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<var>size</var> as needed, and NUL bytes may be embedded in the stream (see
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<code>open_memstream</code> for an alternative that automatically enlarges the
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buffer). When the stream is flushed or closed after a write that
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changed the file size, a NUL byte is written at the current position
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if there is still room; if the stream is not also open for reading, a
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NUL byte is additionally written at the last byte of <var>buf</var> when the
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stream has exceeded <var>size</var>, so that a write-only <var>buf</var> is always
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NUL-terminated when the stream is flushed or closed (and the initial
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<var>size</var> should take this into account). It is not possible to seek
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outside the bounds of <var>size</var>. A NUL byte written during a flush is
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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>size</var>
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is zero or <var>mode</var> is invalid, ENOMEM if <var>buf</var> was NULL and memory
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could not be allocated, 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 being added to POSIX 200x, but is not in POSIX 2001.
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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="fopen.html#fopen" accesskey="n" rel="next">fopen</a>, Previous: <a href="fileno.html#fileno" accesskey="p" rel="prev">fileno</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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