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