man3/open_memstream.3

   1 .\" Copyright 2005 walter harms (walter.harms@informatik.uni-oldenburg.de),
   2 .\" and Copyright 2005, 2012, 2016 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\"
   4 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
   5 .\" Distributed under the GPL.
   6 .\" %%%LICENSE_END
   7 .\"
   8 .\" 2008-12-04, Petr Baudis <pasky@suse.cz>: Document open_wmemstream()
   9 .\"
  10 .TH OPEN_MEMSTREAM 3 2015-03-29 "GNU" "Linux Programmer's Manual"
  11 .SH NAME
  12 open_memstream, open_wmemstream \-  open a dynamic memory buffer stream
  13 .SH SYNOPSIS
  14 .nf
  15 .B #include <stdio.h>
  16
  17 .BI "FILE *open_memstream(char **" ptr ", size_t *" sizeloc );
  18
  19 .B #include <wchar.h>
  20
  21 .BI "FILE *open_wmemstream(wchar_t **" ptr ", size_t *" sizeloc );
  22 .fi
  23 .sp
  24 .in -4n
  25 Feature Test Macro Requirements for glibc (see
  26 .BR feature_test_macros (7)):
  27 .in
  28 .sp
  29 .BR open_memstream (),
  30 .BR open_wmemstream ():
  31 .PD 0
  32 .ad l
  33 .RS 4
  34 .TP 4
  35 Since glibc 2.10:
  36 _POSIX_C_SOURCE\ >=\ 200809L
  37 .TP
  38 Before glibc 2.10:
  39 _GNU_SOURCE
  40 .RE
  41 .ad
  42 .PD
  43 .SH DESCRIPTION
  44 The
  45 .BR open_memstream ()
  46 function opens a stream for writing to a buffer.
  47 The function dynamically allocates the buffer (in the manner of
  48 .BR malloc (3)),
  49 and the buffer automatically grows as required.
  50 After closing the stream, the caller should
  51 .BR free (3)
  52 this buffer.
  53
  54 The locations pointed to by
  55 .IR ptr
  56 and
  57 .I sizeloc
  58 are used to report the current location and size of the buffer.
  59 When the stream is closed
  60 .RB ( fclose (3))
  61 or flushed
  62 .RB ( fflush (3)),
  63 the locations pointed to by
  64 .I ptr
  65 and
  66 .I sizeloc
  67 are updated to contain, respectively, a pointer to the buffer and the
  68 current size of the buffer.
  69 These values remain valid only as long as the caller
  70 performs no further output on the stream.
  71 If further output is performed, then the stream
  72 must again be flushed before trying to access these variables.
  73
  74 A null byte is maintained at the end of the buffer.
  75 This byte is
  76 .I not
  77 included in the size value stored at
  78 .IR sizeloc .
  79
  80 The stream maintains the notion of a current position,
  81 which is initially zero (the start of the buffer).
  82 Each write operation implicitly adjusts the buffer position.
  83 The stream's buffer position can be explicitly changed with
  84 .BR fseek (3)
  85 or
  86 .BR fseeko (3).
  87 Moving the buffer position past the end
  88 of the data already written fills the intervening space with
  89 zeros.
  90
  91 The
  92 .BR open_wmemstream ()
  93 is similar to
  94 .BR open_memstream (),
  95 but operates on wide characters instead of bytes.
  96 .SH RETURN VALUE
  97 Upon successful completion,
  98 .BR open_memstream ()
  99 and
 100 .BR open_wmemstream ()
 101 return a
 102 .I FILE
 103 pointer.
 104 Otherwise, NULL is returned and
 105 .I errno
 106 is set to indicate the error.
 107 .SH VERSIONS
 108 .BR open_memstream ()
 109 was already available in glibc 1.0.x.
 110 .BR open_wmemstream ()
 111 is available since glibc 2.4.
 112 .SH ATTRIBUTES
 113 For an explanation of the terms used in this section, see
 114 .BR attributes (7).
 115 .TS
 116 allbox;
 117 lb lb lb
 118 l l l.
 119 Interface       Attribute       Value
 120 T{
 121 .BR open_memstream (),
 122 .br
 123 .BR open_wmemstream
 124 T}      Thread safety   MT-Safe
 125 .TE
 126
 127 .SH CONFORMING TO
 128 POSIX.1-2008.
 129 These functions are not specified in POSIX.1-2001,
 130 and are not widely available on other systems.
 131 .SH NOTES
 132 There is no file descriptor associated with the file stream
 133 returned by these functions
 134 (i.e.,
 135 .BR fileno (3)
 136 will return an error if called on the returned stream).
 137 .SH BUGS
 138 In glibc before version 2.7, seeking past the end of a stream created by
 139 .BR open_memstream ()
 140 does not enlarge the buffer; instead the
 141 .BR fseek (3)
 142 call fails, returning \-1.
 143 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=1996
 144 .SH EXAMPLE
 145 See
 146 .BR fmemopen (3).
 147 .SH SEE ALSO
 148 .BR fmemopen (3),
 149 .BR fopen (3)