FOPEN(3S) DOMAIN/IX Reference Manual (SYS5) FOPEN(3S)
NAME
fopen, freopen, fdopen - open a stream
USAGE
#include <stdio.h>
FILE *fopen (filename, type)
char *filename, *type;
FILE *freopen (filename, type, stream)
char *filename, *type;
FILE *stream;
FILE *fdopen (fildes, type)
int fildes;
char *type;
DESCRIPTION
Fopen opens the file specified by filename and associates a
stream with it. It then returns a pointer to the FILE
structure associated with the stream.
Filename points to a character string that contains the name
of the file to be opened.
Type is a character string having one of the following
values:
``r'' open for reading
``w'' truncate or create for writing
``a'' append; open for writing at end of file, or
create for writing
``r+'' open for update (reading and writing)
``w+'' truncate or create for update
``a+'' append; open or create for update at end-of-
file
Freopen substitutes filename for the open stream. The ori-
ginal stream is closed, regardless of whether the open ulti-
mately succeeds. Freopen returns a pointer to the FILE
structure associated with stream.
Freopen is used to attach the already open streams associ-
ated with stdin, stdout and stderr to other files.
Fdopen associates a stream with a file descriptor. File
descriptors are obtained from open, dup, creat, or pipe(2),
Printed 5/10/85 FOPEN-1
FOPEN(3S) DOMAIN/IX Reference Manual (SYS5) FOPEN(3S)
which open files but do not return pointers to a FILE struc-
ture stream. Streams are required as input for many of the
Section 3S library routines. The type of stream must agree
with the mode of the open file.
When a file is opened for update, both input and output may
be performed on the resulting stream. However, output may
not be directly followed by input without an intervening
fseek or rewind, and input may not be directly followed by
output without an intervening fseek, rewind, or an input
operation which encounters end-of-file.
When a file is opened for append (i.e., when type is "a" or
"a+"), it is impossible to overwrite information already in
the file. Fseek may be used to reposition the file pointer
to any position in the file, but when output is written to
the file, the current file pointer is disregarded. All out-
put is written at the end of the file and causes the file
pointer to be repositioned at the end of the output. If two
separate processes open the same file for append, each pro-
cess may write freely to the file without fear of destroying
output being written by the other. The output from the two
processes will be intermixed in the file in the order in
which it is written.
DIAGNOSTICS
Fopen and freopen return a NULL pointer on failure.
RELATED INFORMATION
creat(2), dup(2), open(2), pipe(2), fclose(3S), fseek(3S).
FOPEN-2 Printed 5/10/85