359 lines
7.6 KiB
Groff
359 lines
7.6 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)fopen.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd January 30, 2013
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.Dt FOPEN 3
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.Os
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.Sh NAME
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.Nm fopen ,
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.Nm fdopen ,
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.Nm freopen ,
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.Nm fmemopen
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.Nd stream open functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft FILE *
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.Fn fopen "const char * restrict path" "const char * restrict mode"
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.Ft FILE *
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.Fn fdopen "int fildes" "const char *mode"
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.Ft FILE *
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.Fn freopen "const char *path" "const char *mode" "FILE *stream"
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.Ft FILE *
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.Fn fmemopen "void *restrict *buf" "size_t size" "const char * restrict mode"
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.Sh DESCRIPTION
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The
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.Fn fopen
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function
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opens the file whose name is the string pointed to by
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.Fa path
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and associates a stream with it.
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.Pp
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The argument
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.Fa mode
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points to a string beginning with one of the following letters:
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.Bl -tag -width indent
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.It Dq Li r
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Open for reading.
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The stream is positioned at the beginning of the file.
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Fail if the file does not exist.
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.It Dq Li w
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Open for writing.
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The stream is positioned at the beginning of the file.
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Truncate the file to zero length if it exists or create the file if it does not exist.
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.It Dq Li a
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Open for writing.
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The stream is positioned at the end of the file.
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Subsequent writes to the file will always end up at the then current
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end of file, irrespective of any intervening
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.Xr fseek 3
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or similar.
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Create the file if it does not exist.
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.El
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.Pp
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An optional
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.Dq Li +
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following
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.Dq Li r ,
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.Dq Li w ,
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or
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.Dq Li a
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opens the file for both reading and writing.
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An optional
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.Dq Li x
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following
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.Dq Li w
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or
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.Dq Li w+
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causes the
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.Fn fopen
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call to fail if the file already exists.
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An optional
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.Dq Li e
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following the above
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causes the
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.Fn fopen
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call to set the
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.Dv FD_CLOEXEC
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flag on the underlying file descriptor.
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.Pp
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The
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.Fa mode
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string can also include the letter
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.Dq Li b
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after either the
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.Dq Li +
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or the first letter.
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This is strictly for compatibility with
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.St -isoC
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and has effect only for
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.Fn fmemopen ;
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otherwise
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.Dq Li b
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is ignored.
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.Pp
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Any created files will have mode
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.Do Dv S_IRUSR
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\&|
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.Dv S_IWUSR
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\&|
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.Dv S_IRGRP
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\&|
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.Dv S_IWGRP
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\&|
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.Dv S_IROTH
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\&|
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.Dv S_IWOTH Dc
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.Pq Li 0666 ,
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as modified by the process'
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umask value (see
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.Xr umask 2 ) .
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.Pp
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Reads and writes may be intermixed on read/write streams in any order,
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and do not require an intermediate seek as in previous versions of
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.Em stdio .
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This is not portable to other systems, however;
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.Tn ANSI C
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requires that
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a file positioning function intervene between output and input, unless
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an input operation encounters end-of-file.
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.Pp
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The
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.Fn fdopen
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function associates a stream with the existing file descriptor,
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.Fa fildes .
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The mode
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of the stream must be compatible with the mode of the file descriptor.
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The
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.Dq Li x
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mode option is ignored.
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If the
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.Dq Li e
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mode option is present, the
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.Dv FD_CLOEXEC
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flag is set, otherwise it remains unchanged.
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When the stream is closed via
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.Xr fclose 3 ,
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.Fa fildes
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is closed also.
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.Pp
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The
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.Fn freopen
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function
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opens the file whose name is the string pointed to by
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.Fa path
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and associates the stream pointed to by
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.Fa stream
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with it.
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The original stream (if it exists) is closed.
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The
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.Fa mode
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argument is used just as in the
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.Fn fopen
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function.
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.Pp
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If the
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.Fa path
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argument is
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.Dv NULL ,
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.Fn freopen
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attempts to re-open the file associated with
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.Fa stream
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with a new mode.
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The new mode must be compatible with the mode that the stream was originally
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opened with:
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Streams open for reading can only be re-opened for reading,
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streams open for writing can only be re-opened for writing,
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and streams open for reading and writing can be re-opened in any mode.
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The
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.Dq Li x
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mode option is not meaningful in this context.
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.Pp
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The primary use of the
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.Fn freopen
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function
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is to change the file associated with a
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standard text stream
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.Dv ( stderr , stdin ,
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or
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.Dv stdout ) .
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.Pp
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The
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.Fn fmemopen
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function
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associates the buffer given by the
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.Fa buf
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and
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.Fa size
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arguments with a stream.
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The
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.Fa buf
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argument is either a null pointer or point to a buffer that
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is at least
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.Fa size
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bytes long.
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If a null pointer is specified as the
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.Fa buf
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argument,
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.Fn fmemopen
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allocates
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.Fa size
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bytes of memory.
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This buffer is automatically freed when the stream is closed.
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Buffers can be opened in text-mode (default) or binary-mode
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(if
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.Dq Li b
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is present in the second or third position of the
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.Fa mode
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argument).
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Buffers opened in text-mode make sure that writes are terminated with a
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.Dv NULL
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byte, if the last write hasn't filled up the whole buffer.
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Buffers opened in binary-mode never append a
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.Dv NULL
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byte.
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.Sh RETURN VALUES
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Upon successful completion
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.Fn fopen ,
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.Fn fdopen
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and
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.Fn freopen
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return a
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.Tn FILE
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pointer.
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Otherwise,
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.Dv NULL
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is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa mode
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argument
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to
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.Fn fopen ,
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.Fn fdopen ,
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.Fn freopen ,
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or
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.Fn fmemopen
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was invalid.
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.El
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.Pp
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The
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.Fn fopen ,
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.Fn fdopen ,
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.Fn freopen
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and
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.Fn fmemopen
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functions
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may also fail and set
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.Va errno
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for any of the errors specified for the routine
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.Xr malloc 3 .
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.Pp
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The
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.Fn fopen
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function
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may also fail and set
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.Va errno
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for any of the errors specified for the routine
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.Xr open 2 .
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.Pp
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The
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.Fn fdopen
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function
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may also fail and set
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.Va errno
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for any of the errors specified for the routine
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.Xr fcntl 2 .
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.Pp
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The
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.Fn freopen
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function
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may also fail and set
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.Va errno
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for any of the errors specified for the routines
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.Xr open 2 ,
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.Xr fclose 3
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and
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.Xr fflush 3 .
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.Pp
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The
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.Fn fmemopen
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function
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may also fail and set
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.Va errno
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if the
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.Fa size
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argument is 0.
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.Sh SEE ALSO
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.Xr open 2 ,
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.Xr fclose 3 ,
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.Xr fileno 3 ,
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.Xr fseek 3 ,
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.Xr funopen 3
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.Sh STANDARDS
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The
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.Fn fopen
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and
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.Fn freopen
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functions
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conform to
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.St -isoC ,
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with the exception of the
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.Dq Li x
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mode option which conforms to
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.St -isoC-2011 .
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The
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.Fn fdopen
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function
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conforms to
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.St -p1003.1-88 .
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The
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.Dq Li e
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mode option does not conform to any standard
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but is also supported by glibc.
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The
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.Fn fmemopen
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function
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conforms to
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.St -p1003.1-2008 .
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The
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.Dq Li b
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mode does not conform to any standard
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but is also supported by glibc.
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