STDIO_EXT(3) Linux Programmer's Manual STDIO_EXT(3)
__fbufsize, __flbf, __fpending, __fpurge, __freadable, __freading,
__fsetlocking, __fwritable, __fwriting, _flushlbf - interfaces to stdio
size_t __fbufsize(FILE *stream);
size_t __fpending(FILE *stream);
int __flbf(FILE *stream);
int __freadable(FILE *stream);
int __fwritable(FILE *stream);
int __freading(FILE *stream);
int __fwriting(FILE *stream);
int __fsetlocking(FILE *stream, int type);
void __fpurge(FILE *stream);
Solaris introduced routines to allow portable access to the internals
of the FILE structure, and glibc also implemented these.
The __fbufsize() function returns the size of the buffer currently used
by the given stream.
The __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.
The __flbf() function returns a non-zero value if the stream is line-
buffered, and zero otherwise.
The __freadable() function returns a non-zero value if the stream
allows reading, and zero otherwise.
The __fwritable() function returns a non-zero value if the stream
allows writing, and zero otherwise.
The __freading() function returns a non-zero value if the stream is
read-only, or if the last operation on the stream was a read operation,
and zero otherwise.
The __fwriting() function returns a non-zero 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.
The __fsetlocking() function can be used to select the desired type of
locking on the stream. It returns the current type. The type argument
can take the following three values:
Perform implicit locking around every operation on the given
stream (except for the *_unlocked ones). This is the default.
The caller will take care of the locking (possibly using flock-
file(3) in case there is more than one thread), and the stdio
routines will not do locking until the state is reset to FSET-
Don't change the type of locking. (Only return it.)
The _flushlbf() function flushes all line-buffered streams. (Presum-
ably so that output to a terminal is forced out, say before reading
The __fpurge() function discards the contents of the stream's buffer.
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