gno/usr.man/man3/fopen.3

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.\"     @(#)fopen.3	8.1 (Berkeley) 6/4/93
.\"
.TH FOPEN 3 "29 April 1997" GNO "Library Routines"
.SH NAME
.BR fopen ,
.BR fdopen ,
.BR freopen
\- stream open functions
.SH SYNOPSIS
#include <stdio.h>
.sp 1
FILE *\fBfopen\fR(const char *\fIpath\fR, const char *\fImode\fR);
.sp 1
FILE *\fBfdopen\fR(int \fIfildes\fR, const char *\fImode\fR);
.sp 1
FILE *\fBfreopen\fR(const char *\fIpath\fR, const char *\fImode\fR, FILE *\fIstream\fR);
.SH DESCRIPTION
The
.BR fopen 
function
opens the file whose name is the string pointed to by
.I path
and associates a stream with it.
.LP
The argument
.I mode
points to a string beginning with one of the following
sequences (Additional characters may follow these sequences.):
.RS
.IP \fBr\fR
Open text file for reading.
The stream is positioned at the beginning of the file.
.IP \fBr+\fR
Open for reading and writing.
The stream is positioned at the beginning of the file.
.IP \fBw\fR
Truncate file to zero length or create text file for writing.
The stream is positioned at the beginning of the file.
.IP \fBw+\fR
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.
.IP \fBa\fR
Open for writing.
The file is created if it does not exist.
The stream is positioned at the end of the file.
.IP \fBa+\fR
Open for reading and writing.
The file is created if it does not exist.
The stream is positioned at the end of the file.
.RE
.LP
The
.I mode
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.
If the ``b'' is 
.I not 
specified, then the file is assumed to contain text.
On input, carrige returns (``\\r'') will be translated into 
line feeds (``\\n'').
The reverse translation will occur on output.
If the ``b'' 
.I is
specified, no such translation will occur.
.LP
Any created files will have mode
.BR S_IRUSR
\&|
.BR S_IWUSR
\&|
.BR S_IRGRP
\&|
.BR S_IWGRP
\&|
.BR S_IROTH
\&|
.BR S_IWOTH " (0666),"
as modified by the process'
umask value (see
.BR umask (2)).
.LP
The
.BR fdopen 
function associates a stream with the existing file descriptor,
.IR fildes
The
.I mode
of the stream must be compatible with the mode of the file descriptor.
See the section on BUGS.
.LP
The
.BR freopen 
function
opens the file whose name is the string pointed to by
.I path
and associates the stream pointed to by
.I stream
with it.
The original stream (if it exists) is closed.
The
.I mode
argument is used just as in the
.BR fopen 
function.
The primary use of the
.BR freopen 
function
is to change the file associated with a
standard text stream
.IR ( stderr ,
.IR stdin ,
or
.IR stdout  ).
.SH RETURN VALUES
Upon successful completion
.BR fopen ,
.BR fdopen 
and
.BR freopen 
return a FILE
pointer.
Otherwise,
.BR NULL
is returned and the global variable
.IR errno
is set to indicate the error.
.SH ERRORS
.RS
.IP \fBEINVAL\fR
The
.I mode
provided to
.BR fopen ,
.BR fdopen ,
or
.BR freopen 
was invalid.
.RE
.LP
The
.BR fopen ,
.BR fdopen 
and
.BR freopen 
functions
may also fail and set
.IR errno
for any of the errors specified for the routine
.BR malloc (3).
.LP
The
.BR fopen 
function
may also fail and set
.IR errno
for any of the errors specified for the routine
.BR open (2).
.LP
The
.BR fdopen 
function
may also fail and set
.IR errno
for any of the errors specified for the routine
.BR fcntl (2)
or
.BR stat (2).
.LP
The
.BR freopen 
function
may also fail and set
.IR errno
for any of the errors specified for the routines
.BR open (2),
.BR fclose (3)
and
.BR fflush (3).
.SH BUGS
If 
.BR fdopen
is passed a file descriptor in use by another stdio stream (such
as that available from the 
.BR fileno
macro),
the result is currently undefined.
If you need to do such an operation, you should
.BR dup (2)
the result of the 
.BR fileno
macro before passing it to
.BR fdopen .
.LP
Access bits are not currently checked for any file descriptor passed to
.BR fdopen
which is a character-special file.
.SH SEE ALSO
.BR open (2),
.BR stat (2),
.BR fclose (3),
.BR fseek (3),
.BR funopen (3)
.SH STANDARDS
The
.BR fopen 
and
.BR freopen 
functions
conform to ANSI/C.
The
.BR fdopen 
function
conforms to POSIX 1003.1 (1988).