stdlib/FreeBSD/alloca.3

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  28 .\"     @(#)alloca.3    8.1 (Berkeley) 6/4/93
  29 .\" $FreeBSD: src/lib/libc/stdlib/alloca.3,v 1.13 2007/01/09 00:28:09 imp Exp $
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  31 .Dd September 5, 2006
  32 .Dt ALLOCA 3
  33 .Os
  34 .Sh NAME
  35 .Nm alloca
  36 .Nd memory allocator
  37 .Sh SYNOPSIS
  38 .In alloca.h
  39 or
  40 .br
  41 .In stdlib.h
  42 .Ft void *
  43 .Fn alloca "size_t size"
  44 .Sh DESCRIPTION
  45 The
  46 .Fn alloca
  47 macro
  48 allocates
  49 .Fa size
  50 bytes of space in the stack frame of the caller.
  51 This temporary space is automatically freed on
  52 return.
  53 .Sh RETURN VALUES
  54 .Fn alloca
  55 returns a pointer to the beginning of the allocated space.
  56 .Sh SEE ALSO
  57 .Xr brk 2 ,
  58 .Xr calloc 3 ,
  59 .Xr getpagesize 3 ,
  60 .Xr malloc 3 ,
  61 .Xr realloc 3
  62 .Sh HISTORY
  63 .Fn alloca
  64 appeared in
  65 .At 32v .
  66 .\" .Bx ?? .
  67 .\" The function appeared in 32v, pwb and pwb.2 and in 3bsd 4bsd
  68 .\" The first man page (or link to a man page that I can find at the
  69 .\" moment is 4.3...
  70 .Sh BUGS
  71 .Fn alloca
  72 is machine and compiler dependent;
  73 its use is discouraged.
  74 .Pp
  75 .Fn alloca
  76 is slightly unsafe because it cannot ensure that the pointer
  77 returned points to a valid and usable block of memory.
  78 The allocation made may exceed the bounds of the stack, or even go
  79 further into other objects in memory, and
  80 .Fn alloca
  81 cannot determine such an error.
  82 Avoid
  83 .Fn alloca
  84 with large unbounded allocations.
  85 .Pp
  86 The use of C99 variable-length arrays and
  87 .Fn alloca
  88 in the same function will cause the lifetime of alloca's storage to be limited to the block containing the
  89 .Fn alloca