Manpages - stdio_ext.3

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

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

  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 _flushlbf(void);
  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 nonzero value if the stream is line-buffered, and zero otherwise.

The *__freadable*() function returns a nonzero value if the stream allows reading, and zero otherwise.

The *__fwritable*() function returns a nonzero value if the stream allows writing, and zero otherwise.

The *__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.

The *__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.

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:

FSETLOCKING_INTERNAL

Perform implicit locking around every operation on the given stream (except for the *_unlocked ones). This is the default.

FSETLOCKING_BYCALLER

The caller will take care of the locking (possibly using flockfile*(3) in case there is more than one thread), and the stdio routines will not do locking until the state is reset to *FSETLOCKING_INTERNAL.

FSETLOCKING_QUERY

Don’t change the type of locking. (Only return it.)

The *_flushlbf*() function flushes all line-buffered streams. (Presumably so that output to a terminal is forced out, say before reading keyboard input.)

The *__fpurge*() function discards the contents of the stream’s buffer.

For an explanation of the terms used in this section, see *attributes*(7).

*flockfile*(3), *fpurge*(3)

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