FOPEN(2) FOPEN(2)
NAME
fopen, freopen, fdopen, fileno, fclose, sopenr, sopenw,
sclose, fflush, setvbuf, setbuf, fgetpos, ftell, fsetpos,
fseek, rewind, feof, ferror, clearerr - standard buffered
input/output package
SYNOPSIS
#include <u.h>
#include <stdio.h>
FILE *fopen(char *filename, char *mode)
FILE *freopen(char *filename, char *mode, FILE *f)
FILE *fdopen(int fd, char *mode)
int fileno(FILE *f)
FILE *sopenr(char *s)
FILE *sopenw(void)
char *sclose(FILE *f)
int fclose(FILE *f)
int fflush(FILE *f)
int setvbuf(FILE *f, char *buf, int type, long size)
void setbuf(FILE *f, char *buf)
int fgetpos(FILE *f, long *pos)
long ftell(FILE *f)
int fsetpos(FILE *f, long *pos)
int fseek(FILE *f, long offset, int whence)
void rewind(FILE *f)
int feof(FILE *f)
int ferror(FILE *f)
void clearerr(FILE *f)
DESCRIPTION
The functions described in this and related pages (fgetc(2),
Page 1 Plan 9 (printed 11/22/24)
FOPEN(2) FOPEN(2)
fprintf(2), fscanf(2), and tmpfile(2)) implement the ANSI C
buffered I/O package with extensions.
A file with associated buffering is called a stream and is
declared to be a pointer to a defined type FILE. Fopen(2)
creates certain descriptive data for a stream and returns a
pointer to designate the stream in all further transactions.
There are three normally open streams with constant pointers
declared in the include file and associated with the stan-
dard open files:
stdin standard input file
stdout standard output file
stderr standard error file
A constant pointer NULL designates no stream at all.
Fopen opens the file named by filename and associates a
stream with it. Fopen returns a pointer to be used to iden-
tify the stream in subsequent operations, or NULL if the
open fails. Mode is a character string having one of the
following values:
"r" open for reading
"w" truncate to zero length or create for writing
"a" append; open or create for writing at end of file
"r+" open for update (reading and writing)
"w+" truncate to zero length or create for update
"a+" append; open or create for update at end of file
In addition, each of the above strings can have a `b' some-
where after the first character, meaning `binary file', but
this implementation makes no distinction between binary and
text files.
Fclose causes the stream pointed to by f to be flushed (see
below) and does a close (see open(2)) on the associated
file. It frees any automatically allocated buffer. Fclose
is called automatically on exits(2) for all open streams.
Freopen is like open except that it reuses stream pointer f.
Freopen first attempts to close any file associated with f;
it ignores any errors in that close.
Fdopen associates a stream with an open Plan 9 file descrip-
tor.
Fileno returns the number of the Plan 9 file descriptor
associated with the stream.
Sopenr associates a read-only stream with a null-terminated
string.
Page 2 Plan 9 (printed 11/22/24)
FOPEN(2) FOPEN(2)
Sopenw opens a stream for writing. No file descriptor is
associated with the stream; instead, all output is written
to the stream buffer.
Sclose closes a stream opened with sopenr or sopenw. It
returns a pointer to the 0 terminated buffer associated with
the stream.
By default, output to a stream is fully buffered: it is
accumulated in a buffer until the buffer is full, and then
write (see read(2)) is used to write the buffer. An excep-
tion is standard error, which is line buffered: output is
accumulated in a buffer until a newline is written. Input
is also fully buffered by default; this means that read(2)
is used to fill a buffer as much as it can, and then charac-
ters are taken from that buffer until it empties. Setvbuf
changes the buffering method for file f according to type:
either _IOFBF for fully buffered, _IOLBF for line buffered,
or _IONBF for unbuffered (each character causes a read or
write). If buf is supplied, it is used as the buffer and
size should be its size; If buf is zero, a buffer of the
given size is allocated (except for the unbuffered case)
using malloc(2).
Setbuf is an older method for changing buffering. If buf is
supplied, it changes to fully buffered with the given
buffer, which should be of size BUFSIZ (defined in stdio.h).
If buf is zero, the buffering method changes to unbuffered.
Fflush flushes the buffer of output stream f, delivering any
unwritten buffered data to the host file.
There is a file position indicator associated with each
stream. It starts out pointing at the first character
(unless the file is opened with append mode, in which case
the indicator is always ignored). The file position indica-
tor is maintained by the reading and writing functions
described in fgetc(2).
Fgetpos stores the current value of the file position indi-
cator for stream f in the object pointed to by pos. It
returns zero on success, nonzero otherwise. Ftell returns
the current value of the file position indicator. The file
position indicator is to be used only as an argument to
fseek.
Fsetpos sets the file position indicator for stream f to the
value of the object pointed to by pos, which shall be a
value returned by an earlier call to fgetpos on the same
stream. It returns zero on success, nonzero otherwise.
Fseek obtains a new position, measured in characters from
the beginning of the file, by adding offset to the position
Page 3 Plan 9 (printed 11/22/24)
FOPEN(2) FOPEN(2)
specified by whence: the beginning of the file if whence is
SEEK_SET; the current value of the file position indicator
for SEEK_CUR; and the end-of-file for SEEK_END. Rewind sets
the file position indicator to the beginning of the file.
An integer constant EOF is returned upon end of file or
error by integer-valued functions that deal with streams.
Feof returns non-zero if and only if f is at its end of
file.
Ferror returns non-zero if and only if f is in the error
state. It can get into the error state if a system call
failed on the associated file or a memory allocation failed.
Clearerr takes a stream out of the error state.
SOURCE
/sys/src/libstdio
SEE ALSO
fprintf(2), fscanf(2), fgetc(2)
open(2), read(2)
DIAGNOSTICS
The value EOF is returned uniformly to indicate that a FILE
pointer has not been initialized with fopen, input (output)
has been attempted on an output (input) stream, or a FILE
pointer designates corrupt or otherwise unintelligible FILE
data.
Some of these functions set errstr.
BUGS
Buffering of output can prevent output data from being seen
until long after it is computed - perhaps never, as when an
abort occurs between buffer filling and flushing.
Buffering of input can cause a process to consume more input
than it actually uses. This can cause trouble across
exec(2).
Buffering may delay the receipt of a write error until a
subsequent stdio writing, seeking, or file-closing call.
ANSI says that a file can be fully buffered only if the file
is not attached to an interactive device. In Plan 9 all are
fully buffered except standard error.
Fdopen, fileno, sopenr, sopenw, and sclose are not ANSI
Stdio functions.
Stdio offers no support for runes or UTF characters. Unless
external compatibility is necessary, use bio(2), which sup-
ports UTF and is smaller, faster, and simpler than Stdio.
Page 4 Plan 9 (printed 11/22/24)