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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>fopen</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_005_158"> </a>NAME</h4><blockquote>fopen - open a stream</blockquote><h4><a name = "tag_000_005_159"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="stdio.h.html">stdio.h</a>>FILE *fopen(const char *<i>filename</i>, const char *<i>mode</i>);</code></pre></blockquote><h4><a name = "tag_000_005_160"> </a>DESCRIPTION</h4><blockquote>The<i>fopen()</i>function opens the file whose pathname is the string pointed to by<i>filename</i>,and associates a stream with it.<p>The argument<i>mode</i>points to a string beginning with one of the following sequences:<dl compact><dt><b>r</b> or <b>rb</b><dd>Open file for reading.<dt><b>w</b> or <b>wb</b><dd>Truncate to zero length or create file for writing.<dt><b>a</b> or <b>ab</b><dd>Append; open or create file for writing at end-of-file.<dt><b>r+</b> or <b>rb+</b> or <b>r+b</b><dd>Open file for update (reading and writing).<dt><b>w+</b> or <b>wb+</b> or <b>w+b</b><dd>Truncate to zero length or create file for update.<dt><b>a+</b> or <b>ab+</b> or <b>a+b</b><dd>Append; open or create file for update, writing at end-of-file.</dl><p>The character b has no effect, but is allowed for ISO C standardconformance.Opening a file with read mode (r as the first character in the<i>mode</i>argument) fails if the file does not exist or cannot be read.<p>Opening a file with append mode (a as the first character in the<i>mode</i>argument) causes all subsequent writes to the file to be forcedto the then current end-of-file, regardless of intervening callsto<i><a href="fseek.html">fseek()</a></i>.<p>When a file is opened with update mode (+ as the second or thirdcharacter in the<i>mode</i>argument), both input and output may be performed on theassociated stream.However, output must not be directly followed by input without anintervening call to<i><a href="fflush.html">fflush()</a></i>or to a file positioning function (.Fn fseek ,<i><a href="fsetpos.html">fsetpos()</a></i>or<i><a href="rewind.html">rewind()</a></i>),and input must not be directly followed by output without anintervening call to a file positioning function, unless the inputoperation encounters end-of-file.<p>When opened, a stream is fully buffered if and only if it can bedetermined not to refer to an interactive device.The error and end-of-file indicators for the stream are cleared.<p>If<i>mode</i>is <b>w</b>, <b>a</b>, <b>w+</b> or <b>a+</b> and the filedid not previously exist, upon successful completion,<i>fopen()</i>function will mark for update the<i>st_atime</i>,<i>st_ctime</i>and<i>st_mtime</i>fields of the file and the<i>st_ctime</i>and<i>st_mtime</i>fields of the parent directory.<p>If<i>mode</i>is <b>w</b> or <b>w+</b> and the file did previously exist, upon successfulcompletion,<i>fopen()</i>will mark for update the<i>st_ctime</i>and<i>st_mtime</i>fields of the file. The<i>fopen()</i>function will allocate a file descriptor as<i><a href="open.html">open()</a></i>does.<p>The largest value that can be represented correctly in an object of type<b>off_t</b>will be established as the offset maximum in the open file description.</blockquote><h4><a name = "tag_000_005_161"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>fopen()</i>returns a pointer to the object controlling the stream. Otherwise, a nullpointer is returned, and<i>errno</i>is set to indicate the error.<br></blockquote><h4><a name = "tag_000_005_162"> </a>ERRORS</h4><blockquote>The<i>fopen()</i>function will fail if:<dl compact><dt>[EACCES]<dd>Search permission is denied on a component of the path prefix,or the file exists and the permissions specified by<i>mode</i>are denied, or the file does not exist and write permission isdenied for the parent directory of the file to be created.<dt>[EINTR]<dd>A signal was caught during<i>fopen()</i>.<dt>[EISDIR]<dd>The named file is a directory and<i>mode</i>requires write access.<dt>[ELOOP]<dd>Too many symbolic links were encountered in resolving <i>path</i>.<dt>[EMFILE]<dd>{OPEN_MAX} file descriptors are currently open in the calling process.<dt>[ENAMETOOLONG]<dd>The length of the<i>filename</i>exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.<dt>[ENFILE]<dd>The maximum allowable number of files is currently open in the system.<dt>[ENOENT]<dd>A component of <i>filename</i> does not name an existing fileor <i>filename</i> is an empty string.<dt>[ENOSPC]<dd>The directory or file system that would contain thenew file cannot be expanded, the file does not exist, andit was to be created.<dt>[ENOTDIR]<dd>A component of the path prefix is not a directory.<dt>[ENXIO]<dd>The named file is a character special or block special file,and the device associated with this special file does not exist.<dt>[EOVERFLOW]<dd>The named file is a regular file and the size of the file cannot berepresented correctly in an object of type<b>off_t</b>.<dt>[EROFS]<dd>The named file resides on a read-only file system and<i>mode</i>requires write access.</dl><p>The<i>fopen()</i>function may fail if:<dl compact><dt>[EINVAL]<dd>The value of the<i>mode</i>argument is not valid.<dt>[EMFILE]<dd>{FOPEN_MAX} streams are currently open in the calling process.<dt>[EMFILE]<dd>{STREAM_MAX} streams are currently open in the calling process.<dt>[ENAMETOOLONG]<dd>Pathname resolution of a symbolic link produced an intermediate result whoselength exceeds {PATH_MAX}.<dt>[ENOMEM]<dd>Insufficient storage space is available.<dt>[ETXTBSY]<dd>The file is a pure procedure (shared text) file that is being executed and<i>mode</i>requires write access.</dl></blockquote><h4><a name = "tag_000_005_163"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_164"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_165"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_166"> </a>SEE ALSO</h4><blockquote><i><a href="fclose.html">fclose()</a></i>,<i><a href="fdopen.html">fdopen()</a></i>,<i><a href="freopen.html">freopen()</a></i>,<i><a href="stdio.h.html"><stdio.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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