man3/alloca.3

   1 .\" Copyright (c) 1980, 1991 Regents of the University of California.
   2 .\" All rights reserved.
   3 .\"
   4 .\" Redistribution and use in source and binary forms, with or without
   5 .\" modification, are permitted provided that the following conditions
   6 .\" are met:
   7 .\" 1. Redistributions of source code must retain the above copyright
   8 .\"    notice, this list of conditions and the following disclaimer.
   9 .\" 2. Redistributions in binary form must reproduce the above copyright
  10 .\"    notice, this list of conditions and the following disclaimer in the
  11 .\"    documentation and/or other materials provided with the distribution.
  12 .\" 3. All advertising materials mentioning features or use of this software
  13 .\"    must display the following acknowledgement:
  14 .\"     This product includes software developed by the University of
  15 .\"     California, Berkeley and its contributors.
  16 .\" 4. Neither the name of the University nor the names of its contributors
  17 .\"    may be used to endorse or promote products derived from this software
  18 .\"    without specific prior written permission.
  19 .\"
  20 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30 .\" SUCH DAMAGE.
  31 .\"
  32 .\"     @(#)alloca.3    5.1 (Berkeley) 5/2/91
  33 .\"
  34 .\" Converted Mon Nov 29 11:05:55 1993 by Rik Faith <faith@cs.unc.edu>
  35 .\" Modified Tue Oct 22 23:41:56 1996 by Eric S. Raymond <esr@thyrsus.com>
  36 .\" Modified 2002-07-17, aeb
  37 .\"
  38 .TH ALLOCA 3  2002-07-17 "GNU" "Linux Programmer's Manual"
  39 .SH NAME
  40 alloca \- memory allocator
  41 .SH SYNOPSIS
  42 .B #include <alloca.h>
  43 .sp
  44 .BI "void *alloca(size_t " size );
  45 .SH DESCRIPTION
  46 The
  47 .BR alloca ()
  48 function allocates
  49 .I size
  50 bytes of space in the stack frame of the caller.
  51 This temporary space is
  52 automatically freed when the function that called
  53 .BR alloca ()
  54 returns to its caller.
  55 .SH "RETURN VALUE"
  56 The
  57 .BR alloca ()
  58 function returns a pointer to the beginning of the allocated space.
  59 If the allocation causes stack overflow, program behaviour is undefined.
  60 .SH "CONFORMING TO"
  61 There is evidence that the
  62 .BR alloca ()
  63 function appeared in 32v, pwb, pwb.2, 3bsd, and 4bsd.
  64 There is a man page for it in 4.3BSD.
  65 Linux uses the GNU version.
  66 This function is not in POSIX.1-2001.
  67 .SH NOTES
  68 .SS Notes on the GNU Version
  69 Normally,
  70 .B gcc
  71 translates calls to
  72 .BR alloca ()
  73 by inlined code.
  74 This is not done when either the \-ansi or
  75 the \-fno\-builtin option is given.
  76 But beware!
  77 By default the glibc version of
  78 .I <stdlib.h>
  79 includes
  80 .I <alloca.h>
  81 and that contains the line:
  82 .nf
  83
  84     # define alloca(size)   __builtin_alloca (size)
  85
  86 .fi
  87 with messy consequences if one has a private version of this function.
  88 .LP
  89 The fact that the code is inlined, means that it is impossible
  90 to take the address of this function, or to change its behaviour
  91 by linking with a different library.
  92 .LP
  93 The inlined code often consists of a single instruction adjusting
  94 the stack pointer, and does not check for stack overflow.
  95 Thus, there is no NULL error return.
  96 .SH BUGS
  97 The
  98 .BR alloca ()
  99 function is machine and compiler dependent.
 100 On many systems
 101 its implementation is buggy.
 102 Its use is discouraged.
 103 .LP
 104 On many systems
 105 .BR alloca ()
 106 cannot be used inside the list of arguments of a function call, because
 107 the stack space reserved by
 108 .BR alloca ()
 109 would appear on the stack in the middle of the space for the
 110 function arguments.
 111 .SH "SEE ALSO"
 112 .BR brk (2),
 113 .BR pagesize (2),
 114 .BR calloc (3),
 115 .BR malloc (3),
 116 .BR realloc (3)