__FBUFSIZE(3C) Standard C Library Functions __FBUFSIZE(3C)

NAME

__fbufsize, __flbf, __fpending, __fpurge, __freadable, __freading,
__fsetlocking, __fwritable, __fwriting, _flushlbf - interfaces to stdio
FILE structure

SYNOPSIS

#include <stdio.h>
#include <stdio_ext.h>

size_t __fbufsiz(FILE *stream);


int __flbf(FILE *stream);


size_t __fpending(FILE *stream);


void __fpurge(FILE *stream);


int __freadable(FILE *stream);


int __freading(FILE *stream);


int __fsetlocking(FILE *stream, int type);


int __fwritable(FILE *stream);


int __fwriting(FILE *stream);


void _flushlbf(void);

DESCRIPTION

These functions provide portable access to the members of the stdio(3C)
FILE structure.


The __fbufsize() function returns in bytes the size of the buffer
currently in use by the given stream.


The __flbf() function returns non-zero if the stream is line-buffered.


The __fpending function returns in bytes the amount of output pending on
a stream.


The __fpurge() function discards any pending buffered I/O on the stream.


The __freadable() function returns non-zero if it is possible to read
from a stream.


The __freading() function returns non-zero if the file is open readonly,
or if the last operation on the stream was a read operation such as
fread(3C) or fgetc(3C). Otherwise it returns 0.


The __fsetlocking() function allows the type of locking performed by
stdio on a given stream to be controlled by the programmer.


If type is FSETLOCKING_INTERNAL, stdio performs implicit locking around
every operation on the given stream. This is the default system behavior
on that stream.


If type is FSETLOCKING_BYCALLER, stdio assumes that the caller is
responsible for maintaining the integrity of the stream in the face of
access by multiple threads. If there is only one thread accessing the
stream, nothing further needs to be done. If multiple threads are
accessing the stream, then the caller can use the flockfile(),
funlockfile(), and ftrylockfile() functions described on the
flockfile(3C) manual page to provide the appropriate locking. In both
this and the case where type is FSETLOCKING_INTERNAL, __fsetlocking()
returns the previous state of the stream.


If type is FSETLOCKING_QUERY, __fsetlocking() returns the current state
of the stream without changing it.


The __fwritable() function returns non-zero if it is possible to write on
a stream.


The __fwriting() function returns non-zero if the file is open write-only
or append-only, or if the last operation on the stream was a write
operation such as fwrite(3C) or fputc(3C). Otherwise it returns 0.


The _flushlbf() function flushes all line-buffered files. It is used
when reading from a line-buffered file.

USAGE

Although the contents of the stdio FILE structure have always been
private to the stdio implementation, some applications have needed to
obtain information about a stdio stream that was not accessible through a
supported interface. These applications have resorted to accessing fields
of the FILE structure directly, rendering them possibly non-portable to
new implementations of stdio, or more likely, preventing enhancements to
stdio that would cause those applications to break.


In the 64-bit environment, the FILE structure is opaque. The functions
described here are provided as a means of obtaining the information that
up to now has been retrieved directly from the FILE structure. Because
they are based on the needs of existing applications (such as mh and
emacs), they may be extended as other programs are ported. Although they
may still be non-portable to other operating systems, they will be
compatible from each Solaris release to the next. Interfaces that are
more portable are under development.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+----------------------------+
|MT-Level | __fsetlocking() is Unsafe; |
| | all others are MT-Safe |
+--------------------+----------------------------+
|Interface Stability | Evolving |
+--------------------+----------------------------+

SEE ALSO

fgetc(3C), flockfile(3C), fputc(3C), fread(3C), fwrite(3C), stdio(3C),
attributes(7)


February 5, 1998 __FBUFSIZE(3C)