plan9fox/sys/man/2/fopen

.TH FOPEN 2
.SH 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
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <stdio.h>
.PP
.ta \w'\fLFILE 'u
.B
FILE	*fopen(char *filename, char *mode)
.PP
.B
FILE	*freopen(char *filename, char *mode, FILE *f)
.PP
.B
FILE	*fdopen(int fd, char *mode)
.PP
.B
int	fileno(FILE *f)
.PP
.B
FILE	*sopenr(char *s)
.PP
.B
FILE	*sopenw(void)
.PP
.B
char	*sclose(FILE *f)
.PP
.B
int	fclose(FILE *f)
.PP
.B
int	fflush(FILE *f)
.PP
.B
int	setvbuf(FILE *f, char *buf, int type, long size)
.PP
.B
void	setbuf(FILE *f, char *buf)
.PP
.B
int	fgetpos(FILE *f, long *pos)
.PP
.B
long	ftell(FILE *f)
.PP
.B
int	fsetpos(FILE *f, long *pos)
.PP
.B
int	fseek(FILE *f, long offset, int whence)
.PP
.B
void	rewind(FILE *f)
.PP
.B
int	feof(FILE *f)
.PP
.B
int	ferror(FILE *f)
.PP
.B
void	clearerr(FILE *f)
.SH DESCRIPTION
The functions described in this and related pages
.RI ( fgetc (2),
.IR fprintf (2),
.IR fscanf (2),
and
.IR tmpfile (2))
implement the
ANSI C buffered I/O package with extensions.
.PP
A file with associated buffering is called a
.I stream
and is declared to be a pointer to a defined type
.BR FILE .
.IR  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 standard open files:
.TP 10n
.BR stdin
standard input file
.br
.ns
.TP
.B stdout
standard output file
.br
.ns
.TP
.B stderr
standard error file
.PP
A constant pointer
.B NULL
designates no stream at all.
.PP
.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, or
.B NULL
if the open fails.
.I Mode
is a character string having one of the following values:
.nf
.ta 8n
\fL"r"\fP	open for reading
\fL"w"\fP	truncate to zero length or create for writing
\fL"a"\fP	append; open or create for writing at end of file
\fL"r+"\fP	open for update (reading and writing)
\fL"w+"\fP	truncate to zero length or create for update
\fL"a+"\fP	append; open or create for update at end of file
.fi
.PP
In addition, each of the above strings can have a
.L b
somewhere after the first character,
meaning `binary file', but this implementation makes no distinction
between binary and text files.
.PP
.I Fclose
causes the stream pointed to by
.I f
to be flushed (see below) and does a
.I close
(see
.IR open (2))
on the associated file.
It frees any automatically allocated buffer.
.I Fclose
is called automatically on 
.IR exits (2)
for all open streams.
.PP
.I Freopen
is like open except that it reuses stream pointer
.IR f .
.I Freopen
first attempts to close any file associated with
.IR f ;
it ignores any errors in that close.
.PP
.I Fdopen
associates a stream with an open Plan 9 file descriptor.
.PP
.I Fileno
returns the number of the Plan 9 file descriptor associated with the stream.
.PP
.I Sopenr
associates a read-only stream with a null-terminated string. 
.PP
.I Sopenw
opens a stream for writing.
No file descriptor is associated with the stream;
instead, all output is written to the stream buffer.
.PP
.I Sclose
closes a stream opened with
.I sopenr
or
.IR sopenw .
It returns a pointer to the 0 terminated buffer associated with the stream.
.PP
By default, output to a stream is fully buffered: it is accumulated in
a buffer until the buffer is full, and then
.I write
(see
.IR read (2))
is used to write the buffer.
An exception 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
.IR read (2)
is used to fill a buffer as much as it can, and then characters
are taken from that buffer until it empties.
.I Setvbuf
changes the buffering method for file
.I f
according to
.IR type:
either
.B _IOFBF
for fully buffered,
.B _IOLBF
for line buffered,
or
.B _IONBF
for unbuffered (each character causes a
.I read
or
.IR write).
If
.I buf
is supplied, it is used as the buffer and
.I size
should be its size;
If
.I buf
is zero, a buffer of the given size is allocated (except for the unbuffered case) using
.IR malloc (2).
.PP
.I Setbuf
is an older method for changing buffering.  If
.I buf
is supplied, it changes to fully buffered with the given buffer, which should
be of size
.B BUFSIZ
(defined in
.BR stdio.h ).
If
.I buf
is zero, the buffering method changes to unbuffered.
.PP
.I Fflush
flushes the buffer of output stream
.IR f ,
delivering any unwritten buffered data to the host file.
.PP
There is a
.I 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 indicator is maintained by the reading and writing
functions described in
.IR fgetc (2).
.PP
.I Fgetpos
stores the current value of the file position indicator for stream
.I f
in the object pointed to by
.IR pos .
It returns zero on success, nonzero otherwise.
.I Ftell
returns the current value of the file position indicator.
The file position indicator is to
be used only as an argument to
.IR fseek.
.PP
.I Fsetpos
sets the file position indicator for stream
.I f
to the value of the object pointed to by
.IR pos ,
which shall be a value returned by an earlier call to
.I fgetpos
on the same stream.
It returns zero on success, nonzero otherwise.
.I Fseek
obtains a new position, measured in characters from the beginning
of the file, by adding
.I offset
to the position specified by
.IR whence :
the beginning of the file if
.I whence
is
.BR SEEK_SET ;
the current value of the file position indicator for
.BR SEEK_CUR ;
and the end-of-file for
.BR SEEK_END .
.I Rewind
sets the file position indicator to the beginning of the file.
.PP
An integer constant
.B EOF
is returned
upon end of file or error by integer-valued functions that
deal with streams.
.I Feof
returns non-zero if and only if
.I f
is at its end of file.
.PP
.I Ferror
returns non-zero if and only if
.I 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.
.I Clearerr
takes a stream out of the error state.
.SH SOURCE
.B /sys/src/libstdio
.SH "SEE ALSO"
.IR fprintf (2),
.IR fscanf (2),
.IR fgetc (2)
.br
.IR open (2), 
.IR read (2)
.SH DIAGNOSTICS
The value
.B EOF
is returned uniformly to indicate that a
.B FILE
pointer has not been initialized with
.IR fopen ,
input (output) has been attempted on an output (input) stream,
or a
.B FILE
pointer designates corrupt or otherwise unintelligible
.B FILE
data.
.br
Some of these functions set
.IR errstr .
.SH 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.
.br
Buffering of input can cause a process to consume
more input than it actually uses.
This can cause trouble across
.IR exec (2).
.br
Buffering may delay the receipt of a write error until a subsequent
.I stdio
writing, seeking, or file-closing call.
.br
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.
.PP
.IR Fdopen ,
.IR fileno , 
.IR sopenr , 
.IR sopenw ,
and
.I sclose
are not ANSI Stdio functions.
.PP
Stdio offers no support for runes or
.SM UTF
characters.
Unless external compatibility is necessary, use
.IR bio (2),
which supports
.SM UTF
and is smaller, faster, and simpler than Stdio.