view doc/alloca.texi @ 7376:5b76a3b030e7

author Karl Berry <>
date Wed, 27 Sep 2006 07:37:50 +0000
parents adb21c293305
children 6bc27027a2d6
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@c Documentation of gnulib module 'alloca'.

@c Copyright (C) 2004 Free Software Foundation, Inc.

@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.2 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
@c Texts.  A copy of the license is included in the ``GNU Free
@c Documentation License'' file as part of this distribution.

The alloca module provides for a function alloca() which allocates memory
on the stack, where the system allows it. A memory block allocated with alloca()
exists only until the function that calls alloca() returns or exits abruptly.

There are a few systems where this is not possible: HP-UX systems, and some
other platforms when the C++ compiler is used. On these platforms the alloca
module provides a malloc() based emulation. This emulation will not free a
memory block immediately when the calling function returns, but rather will
wait until the next alloca() call from a function with the same or a shorter
stack length. Thus, in some cases, a few memory blocks will be kept although
they are not needed any more.

The user can #include <alloca.h> and use alloca() on all platforms. Note
that the #include <alloca.h> must be the first one after the autoconf-generated
config.h. Thanks to AIX for this nice restriction!

An alternative to this module is the 'alloca-opt' module.