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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FOPEN" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fopen 
.SH NAME
fopen \- open a stream
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
.sp
FILE *fopen(const char *restrict\fP \fIfilename\fP\fB, const char
*restrict\fP \fImode\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIfopen\fP() function shall open the file whose pathname is the
string pointed to by \fIfilename\fP, and associates a
stream with it.
.LP
The \fImode\fP argument points to a string. If the string is one of
the following, the file shall be opened in the indicated
mode. Otherwise, the behavior is undefined.
.TP 7
\fIr\fP\ or\ \fIrb\fP
Open file for reading.
.TP 7
\fIw\fP\ or\ \fIwb\fP
Truncate to zero length or create file for writing.
.TP 7
\fIa\fP\ or\ \fIab\fP
Append; open or create file for writing at end-of-file.
.TP 7
\fIr+\fP\ or\ \fIrb+\fP\ or\ \fIr+b\fP
Open file for update (reading and writing).
.TP 7
\fIw+\fP\ or\ \fIwb+\fP\ or\ \fIw+b\fP
Truncate to zero length or create file for update.
.TP 7
\fIa+\fP\ or\ \fIab+\fP\ or\ \fIa+b\fP
Append; open or create file for update, writing at end-of-file.
.sp
.LP
The
character \fB'b'\fP shall have no effect, but is allowed for ISO\ C
standard conformance.  Opening a file with read mode (\fIr\fP as the
first character in the \fImode\fP argument) shall
fail if the file does not exist or cannot be read.
.LP
Opening a file with append mode (\fIa\fP as the first character in
the \fImode\fP argument) shall cause all subsequent writes
to the file to be forced to the then current end-of-file, regardless
of intervening calls to \fIfseek\fP().
.LP
When a file is opened with update mode ( \fB'+'\fP as the second or
third character in the \fImode\fP argument), both input
and output may be performed on the associated stream. However, the
application shall ensure that output is not directly followed by
input without an intervening call to \fIfflush\fP() or to a file positioning
function ( \fIfseek\fP(), \fIfsetpos\fP(), or \fIrewind\fP()), and
input is not directly followed by output without an intervening call
to a file
positioning function, unless the input operation encounters end-of-file.
.LP
When opened, a stream is fully buffered if and only if it can be determined
not to refer to an interactive device. The error and
end-of-file indicators for the stream shall be cleared.
.LP
If
\fImode\fP is \fIw\fP, \fIwb\fP, \fIa\fP, \fIab\fP, \fIw\fP+, \fIwb\fP+,
\fIw\fP+\fIb\fP, \fIa\fP+, \fIab\fP+, or
\fIa\fP+\fIb\fP, and the file did not previously exist, upon successful
completion, the \fIfopen\fP() function shall mark for
update the \fIst_atime\fP, \fIst_ctime\fP, and \fIst_mtime\fP fields
of the file and the \fIst_ctime\fP and \fIst_mtime\fP
fields of the parent directory.
.LP
If \fImode\fP is \fIw\fP, \fIwb\fP, \fIw\fP+, \fIwb\fP+, or \fIw\fP+\fIb\fP,
and the file did previously exist, upon
successful completion, \fIfopen\fP() shall mark for update the \fIst_ctime\fP
and \fIst_mtime\fP fields of the file. The
\fIfopen\fP() function shall allocate a file descriptor as \fIopen\fP()
does. 
.LP
After a successful call to the \fIfopen\fP() function, the orientation
of the stream shall be cleared,   \ the encoding
rule shall be cleared,  and the associated \fBmbstate_t\fP object
shall be set to describe an initial conversion state.
.LP
The
largest value that can be represented correctly in an object of type
\fBoff_t\fP shall be established as the offset maximum in the
open file description. 
.SH RETURN VALUE
.LP
Upon successful completion, \fIfopen\fP() shall return a pointer to
the object controlling the stream. Otherwise, a null
pointer shall be returned,   \ and \fIerrno\fP shall be set to indicate
the error. 
.SH ERRORS
.LP
The \fIfopen\fP() function shall fail if:
.TP 7
.B EACCES
Search permission is denied on a component of the path prefix, or
the file exists and the permissions specified by \fImode\fP are
denied, or the file does not exist and write permission is denied
for the parent directory of the file to be created. 
.TP 7
.B EINTR
A
signal was caught during \fIfopen\fP(). 
.TP 7
.B EISDIR
The named file is a directory and \fImode\fP requires write access.
.TP 7
.B ELOOP
A
loop exists in symbolic links encountered during resolution of the
\fIpath\fP argument. 
.TP 7
.B EMFILE
{OPEN_MAX} file descriptors are currently open in the calling process.
.TP 7
.B ENAMETOOLONG
.sp
The length of the \fIfilename\fP argument exceeds {PATH_MAX} or a
pathname component is longer than {NAME_MAX}. 
.TP 7
.B ENFILE
The maximum allowable number of files is currently open in the system.
.TP 7
.B ENOENT
A
component of \fIfilename\fP does not name an existing file or \fIfilename\fP
is an empty string. 
.TP 7
.B ENOSPC
The directory or file system that would contain the new file cannot
be expanded, the file does not exist, and the file was to be
created. 
.TP 7
.B ENOTDIR
A
component of the path prefix is not a directory. 
.TP 7
.B ENXIO
The named file is a character special or block special file, and the
device associated with this special file does not exist. 
.TP 7
.B EOVERFLOW
The named file is a regular file and the size of the file cannot be
represented correctly in an object of type \fBoff_t\fP. 
.TP 7
.B EROFS
The named file resides on a read-only file system and \fImode\fP requires
write access. 
.sp
.LP
The \fIfopen\fP() function may fail if:
.TP 7
.B EINVAL
The value of the \fImode\fP argument is not valid. 
.TP 7
.B ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution
of the \fIpath\fP argument. 
.TP 7
.B EMFILE
{FOPEN_MAX} streams are currently open in the calling process. 
.TP 7
.B EMFILE
{STREAM_MAX} streams are currently open in the calling process. 
.TP 7
.B ENAMETOOLONG
.sp
Pathname resolution of a symbolic link produced an intermediate result
whose length exceeds {PATH_MAX}. 
.TP 7
.B ENOMEM
Insufficient storage space is available. 
.TP 7
.B ETXTBSY
The file is a pure procedure (shared text) file that is being executed
and \fImode\fP requires write access. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Opening a File
.LP
The following example tries to open the file named \fBfile\fP for
reading. The \fIfopen\fP() function returns a file pointer
that is used in subsequent \fIfgets\fP() and \fIfclose\fP() calls.
If the program cannot open the file, it just ignores it.
.sp
.RS
.nf

\fB#include <stdio.h>
\&...
FILE *fp;
\&...
void rgrep(const char *file)
{
\&...
    if ((fp = fopen(file, "r")) == NULL)
        return;
\&...
}
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIfclose\fP() , \fIfdopen\fP() , \fIfreopen\fP() , the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, \fI<stdio.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .