man3/stdio_ext.3

   1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .TH STDIO_EXT 3 2021-03-22 "" "Linux Programmer's Manual"
   6 .SH NAME
   7 __fbufsize, __flbf, __fpending, __fpurge, __freadable,
   8 __freading, __fsetlocking, __fwritable, __fwriting, _flushlbf \-
   9 interfaces to stdio FILE structure
  10 .SH LIBRARY
  11 Standard C library
  12 .RI ( libc ", " \-lc )
  13 .SH SYNOPSIS
  14 .nf
  15 .B #include <stdio.h>
  16 .B #include <stdio_ext.h>
  17 .PP
  18 .BI "size_t __fbufsize(FILE *" stream );
  19 .BI "size_t __fpending(FILE *" stream );
  20 .BI "int __flbf(FILE *" stream );
  21 .BI "int __freadable(FILE *" stream );
  22 .BI "int __fwritable(FILE *" stream );
  23 .BI "int __freading(FILE *" stream );
  24 .BI "int __fwriting(FILE *" stream );
  25 .BI "int __fsetlocking(FILE *" stream ", int " type );
  26 .B "void _flushlbf(void);"
  27 .BI "void __fpurge(FILE *" stream );
  28 .fi
  29 .SH DESCRIPTION
  30 Solaris introduced routines to allow portable access to the
  31 internals of the
  32 .I FILE
  33 structure, and glibc also implemented these.
  34 .PP
  35 The
  36 .BR __fbufsize ()
  37 function returns the size of the buffer currently used
  38 by the given stream.
  39 .PP
  40 The
  41 .BR __fpending ()
  42 function returns the number of bytes in the output buffer.
  43 For wide-oriented streams the unit is wide characters.
  44 This function is undefined on buffers in reading mode,
  45 or opened read-only.
  46 .PP
  47 The
  48 .BR __flbf ()
  49 function returns a nonzero value if the stream is line-buffered,
  50 and zero otherwise.
  51 .PP
  52 The
  53 .BR __freadable ()
  54 function returns a nonzero value if the stream allows reading,
  55 and zero otherwise.
  56 .PP
  57 The
  58 .BR __fwritable ()
  59 function returns a nonzero value if the stream allows writing,
  60 and zero otherwise.
  61 .PP
  62 The
  63 .BR __freading ()
  64 function returns a nonzero value if the stream is read-only, or
  65 if the last operation on the stream was a read operation,
  66 and zero otherwise.
  67 .PP
  68 The
  69 .BR __fwriting ()
  70 function returns a nonzero value if the stream is write-only (or
  71 append-only), or if the last operation on the stream was a write
  72 operation, and zero otherwise.
  73 .PP
  74 The
  75 .BR __fsetlocking ()
  76 function can be used to select the desired type of locking on the stream.
  77 It returns the current type.
  78 The
  79 .I type
  80 argument can take the following three values:
  81 .TP
  82 .B FSETLOCKING_INTERNAL
  83 Perform implicit locking around every operation on the given stream
  84 (except for the *_unlocked ones).
  85 This is the default.
  86 .TP
  87 .B FSETLOCKING_BYCALLER
  88 The caller will take care of the locking (possibly using
  89 .BR flockfile (3)
  90 in case there is more than one thread), and the stdio routines
  91 will not do locking until the state is reset to
  92 .BR FSETLOCKING_INTERNAL .
  93 .TP
  94 .B FSETLOCKING_QUERY
  95 Don't change the type of locking.
  96 (Only return it.)
  97 .PP
  98 The
  99 .BR _flushlbf ()
 100 function flushes all line-buffered streams.
 101 (Presumably so that
 102 output to a terminal is forced out, say before reading keyboard input.)
 103 .PP
 104 The
 105 .BR __fpurge ()
 106 function discards the contents of the stream's buffer.
 107 .SH ATTRIBUTES
 108 For an explanation of the terms used in this section, see
 109 .BR attributes (7).
 110 .ad l
 111 .nh
 112 .TS
 113 allbox;
 114 lbx lb lb
 115 l l l.
 116 Interface       Attribute       Value
 117 T{
 118 .BR __fbufsize (),
 119 .BR __fpending (),
 120 .BR __fpurge (),
 121 .BR __fsetlocking ()
 122 T}      Thread safety   MT-Safe race:stream
 123 T{
 124 .BR __flbf (),
 125 .BR __freadable (),
 126 .BR __freading (),
 127 .BR __fwritable (),
 128 .BR __fwriting (),
 129 .BR _flushlbf ()
 130 T}      Thread safety   MT-Safe
 131 .TE
 132 .hy
 133 .ad
 134 .sp 1
 135 .SH SEE ALSO
 136 .BR flockfile (3),
 137 .BR fpurge (3)