minix/lib/libc/stdlib/alloca.3

.\"	$NetBSD: alloca.3,v 1.14 2011/03/21 04:42:50 jruoho Exp $
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.\"     from: @(#)alloca.3	8.1 (Berkeley) 6/4/93
.\"
.Dd March 21, 2011
.Dt ALLOCA 3
.Os
.Sh NAME
.Nm alloca
.Nd memory allocator
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft void *
.Fn alloca "size_t size"
.Sh DESCRIPTION
The
.Fn alloca
function
allocates
.Fa size
bytes of space in the stack frame of the caller.
This temporary space is automatically freed on
return.
.Sh RETURN VALUES
The
.Fn alloca
function returns a pointer to the beginning of the allocated space.
If the allocation failed, a
.Dv NULL
pointer is returned.
.Sh SEE ALSO
.Xr brk 2 ,
.Xr calloc 3 ,
.Xr getpagesize 3 ,
.Xr malloc 3 ,
.Xr realloc 3
.Sh CAVEATS
Few limitations can be mentioned:
.Bl -bullet
.It
The
.Fn alloca
function
is machine dependent; its use is discouraged.
.It
The
.Fn alloca
function is slightly unsafe because it cannot ensure that the pointer
returned points to a valid and usable block of memory.
The allocation made may exceed the bounds of the stack, or even go
further into other objects in memory, and
.Fn alloca
cannot determine such an error.
Avoid
.Fn alloca
with large unbounded allocations.
.It
Since
.Fn alloca
modifies the stack at runtime,
it causes problems to certain security features.
See
.Xr security 7
for a discussion.
.El
.\" .Sh HISTORY
.\" The
.\" .Fn alloca
.\" function appeared in
.\" .Bx ?? .
.\" The function appeared in 32v, pwb and pwb.2 and in 3bsd 4bsd
.\" The first man page (or link to a man page that I can find at the
.\" moment is 4.3...