.\" Copyright (c) 1990 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek.
.\"
.\" %sccs.include.redist.man%
.\"
.\"	@(#)fopen.3	6.6 (Berkeley) %G%
.\"
.TH FOPEN 3 ""
.UC 7
.SH NAME
fopen, fdopen, freopen \- open a stream
.SH SYNOPSIS
.nf
.ft B
#include <stdio.h>

FILE *
fopen(char *path, char *type);

FILE *
fdopen(int fildes, char *type);

FILE *
freopen(char *path, char *type, FILE *stream);
.ft R
.fi
.SH DESCRIPTION
.I Fopen
opens the file named by
.I path
and associates a stream with it, returning a pointer for identifying
the stream in subsequent operations.
.PP
.I Type
is one of the following character strings:
.TP
``r''
Open for reading.
The stream is positioned at the beginning of the file.
.TP
``r+''
Open for reading and writing.
The stream is positioned at the beginning of the file.
.TP
``w''
Open for writing.
The file is created if it does not exist, otherwise it is truncated.
The stream is positioned at the beginning of the file.
.TP
``w+''
Open for reading and writing.
The file is created if it does not exist, otherwise it is truncated.
The stream is positioned at the beginning of the file.
.TP
``a''
Open for writing.
The file is created if it does not exist.
The stream is positioned at the end of the file.
.TP
``a+''
Open for reading and writing.
The file is created if it does not exist.
The stream is positioned at the end of the file.
.PP
The
.I type
string can also include the letter ``b'' either as a third character or
as a character between the characters in any of the two-character strings
described above.
This is strictly for compatibility with ANSI X3.159-1989 (``ANSI C'')
and has no effect; the ``b'' is ignored.
.PP
Any created files will have mode ``S_IRUSR  |  S_IWUSR | S_IRGRP | 
S_IWGRP | S_IROTH | S_IWOTH'' (0666), as modified by the process'
umask value (see
.IR umask (2)).
.PP
Reads and writes may be intermixed on read/write streams in any order,
and do not require an intermediate seek as in previous versions of 
stdio.
This is not portable to other systems, however; ANSI C requires that
a file positioning function intervene between output and input, unless
an input operation encounters end-of-file.
.PP
.I Fdopen
associates a stream with a file descriptor obtained from
.IR creat (2),
.IR dup (2),
.IR open (2),
or
.IR pipe (2).
The
.I type
of the stream must be compatible with the mode of the file descriptor.
.PP
.I Freopen
substitutes the named file in place of the open
.IR stream 
and returns a pointer to it.
The original stream is closed.
.I Freopen
is typically used to attach the preopened constant names,
.IR stdin ,
.IR stdout ,
and
.I stderr
to files.
.SH "SEE ALSO"
open(2), fclose(3), fseek(3), funopen(3)
.SH "RETURN VALUES"
Upon successful completion 
.IR fopen ,
.I fdopen
and
.I freopen
return a FILE pointer.
Otherwise, NULL is returned and the global variable
.I errno
is set to indicate the error.
.SH ERRORS
.TP 15 
[EINVAL]
The 
.I type
provided to 
.IR fopen ,
.IR fdopen ,
or
.IR freopen 
was invalid.
.PP
.IR Fopen ,
.I fdopen
and
.I freopen
may also fail and set
.IR errno
for any of the errors specified for the routine
.IR malloc (3).
.PP
.I Fopen
may also fail and set
.IR errno
for any of the errors specified for the routine
.IR open (2).
.PP
.I Fdopen
may also fail and set
.IR errno
for any of the errors specified for the routine
.IR fcntl (2).
.PP
.I Freopen
may also fail and set
.IR errno
for any of the errors specified for the routines
.IR open (2), 
.IR fclose (3)
and
.IR fflush (3).
.SH STANDARDS
.I Fopen
and
.I freopen
conform to ANSI X3.159-1989 (``ANSI C'').
.I Fdopen
conforms to IEEE Std 1003.1-1988 (``POSIX'').
.SH BUGS
.I Fdopen
may not be portable to systems other than UNIX.