'\" t
.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH stdio_ext 3 2023-01-07 "Linux man-pages 6.04"
.SH NAME
__fbufsize, __flbf, __fpending, __fpurge, __freadable,
__freading, __fsetlocking, __fwritable, __fwriting, _flushlbf \-
interfaces to stdio FILE structure
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.B #include <stdio_ext.h>
.PP
.BI "size_t __fbufsize(FILE *" stream );
.BI "size_t __fpending(FILE *" stream );
.BI "int __flbf(FILE *" stream );
.BI "int __freadable(FILE *" stream );
.BI "int __fwritable(FILE *" stream );
.BI "int __freading(FILE *" stream );
.BI "int __fwriting(FILE *" stream );
.BI "int __fsetlocking(FILE *" stream ", int " type );
.B "void _flushlbf(void);"
.BI "void __fpurge(FILE *" stream );
.fi
.SH DESCRIPTION
Solaris introduced routines to allow portable access to the
internals of the
.I FILE
structure, and glibc also implemented these.
.PP
The
.BR __fbufsize ()
function returns the size of the buffer currently used
by the given stream.
.PP
The
.BR __fpending ()
function returns the number of bytes in the output buffer.
For wide-oriented streams the unit is wide characters.
This function is undefined on buffers in reading mode,
or opened read-only.
.PP
The
.BR __flbf ()
function returns a nonzero value if the stream is line-buffered,
and zero otherwise.
.PP
The
.BR __freadable ()
function returns a nonzero value if the stream allows reading,
and zero otherwise.
.PP
The
.BR __fwritable ()
function returns a nonzero value if the stream allows writing,
and zero otherwise.
.PP
The
.BR __freading ()
function returns a nonzero value if the stream is read-only, or
if the last operation on the stream was a read operation,
and zero otherwise.
.PP
The
.BR __fwriting ()
function returns a nonzero value if the stream is write-only (or
append-only), or if the last operation on the stream was a write
operation, and zero otherwise.
.PP
The
.BR __fsetlocking ()
function can be used to select the desired type of locking on the stream.
It returns the current type.
The
.I type
argument can take the following three values:
.TP
.B FSETLOCKING_INTERNAL
Perform implicit locking around every operation on the given stream
(except for the *_unlocked ones).
This is the default.
.TP
.B FSETLOCKING_BYCALLER
The caller will take care of the locking (possibly using
.BR flockfile (3)
in case there is more than one thread), and the stdio routines
will not do locking until the state is reset to
.BR FSETLOCKING_INTERNAL .
.TP
.B FSETLOCKING_QUERY
Don't change the type of locking.
(Only return it.)
.PP
The
.BR _flushlbf ()
function flushes all line-buffered streams.
(Presumably so that
output to a terminal is forced out, say before reading keyboard input.)
.PP
The
.BR __fpurge ()
function discards the contents of the stream's buffer.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR __fbufsize (),
.BR __fpending (),
.BR __fpurge (),
.BR __fsetlocking ()
T}	Thread safety	MT-Safe race:stream
T{
.BR __flbf (),
.BR __freadable (),
.BR __freading (),
.BR __fwritable (),
.BR __fwriting (),
.BR _flushlbf ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH SEE ALSO
.BR flockfile (3),
.BR fpurge (3)