V10/man/adm/man3/fopen.3

.TH FOPEN 3S
.CT 2 file_io
.SH NAME
fopen, freopen, fdopen, fclose, fflush \(mi open, close, or flush a stream
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.PP
.B FILE *fopen(filename, type)
.B char *filename, *type;
.PP
.B FILE *freopen(filename, type, stream)
.B char *filename, *type;
.B FILE *stream;
.PP
.B FILE *fdopen(fildes, type)
.B char *type;
.PP
.B int fclose(stream)
.B FILE *stream;
.PP
.B int fflush(stream)
.B FILE *stream;
.fi
.SH DESCRIPTION
.I Fopen
opens the file named by
.I filename
and associates a stream with it.
.I Fopen
returns a pointer to be used to identify
the stream in subsequent operations.
.PP
.I Type
is a character string having one of the following values:
.nf
.ta 8n
\fL"r"\fP	open for reading
\fL"w"\fP	create for writing
\fL"r+w"\fP
\fL"w+r"\fP	open for reading and writing
\fL"a"\fP	append: open for writing at end of file, or create for writing
.fi
.PP
.I Freopen
substitutes the named file in place
of the open
.IR stream .
It returns the original value of
.IR stream .
The original stream is closed.
.I Freopen
is typically used to attach the preopened
constant names
.LR stdin ,
.L stdout
and
.L stderr
to specified files.
.PP
.I Fdopen
associates a stream with a file descriptor.
The
.I type
of the stream must agree with the mode of the open file.
.PP
.I Fclose
causes any buffers for the named
.I stream
to be emptied, and the file to be closed.
Buffers allocated by the standard input/output system
are freed.
.PP
.I Fclose
is performed automatically upon
calling
.IR  exit (3).
.PP
.I Fflush
causes any buffered data for the named output
.I stream
to be written to that file.
The stream remains open.
.SH "SEE ALSO"
.IR open (2),
.IR popen (3),
.IR stdio (3),
.IR ferror (3)
.SH DIAGNOSTICS
.I Fopen
and
.I freopen
return
.B NULL
if
.I filename
cannot be accessed.
.PP
.I Fclose
and
.I fflush
return
.B EOF
if
.I stream
is not associated with a file, or
if buffered data cannot be transferred to that file.