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 __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);

DESCRIPTION

       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.

ATTRIBUTES

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

       ┌───────────────────────────────────────────────────┬───────────────┬─────────────────────┐
       │Interface                                          │ Attribute     │ Value               │
       ├───────────────────────────────────────────────────┼───────────────┼─────────────────────┤
       │__fbufsize(), __fpending(), __fpurge(),            │ Thread safety │ MT-Safe race:stream │
       │__fsetlocking()                                    │               │                     │
       ├───────────────────────────────────────────────────┼───────────────┼─────────────────────┤
       │__flbf(), __freadable(), __freading(),             │ Thread safety │ MT-Safe             │
       │__fwritable(), __fwriting(), _flushlbf()           │               │                     │
       └───────────────────────────────────────────────────┴───────────────┴─────────────────────┘

SEE ALSO

       flockfile(3), fpurge(3)

COLOPHON

       This  page  is  part of release 5.13 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.

                                            2021-03-22                               STDIO_EXT(3)