1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. 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.\" 4. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 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 $ 30.\" $DragonFly: src/lib/libc/stdlib/alloca.3,v 1.2 2003/06/17 04:26:46 dillon Exp $ 31.\" 32.Dd September 5, 2006 33.Dt ALLOCA 3 34.Os 35.Sh NAME 36.Nm alloca 37.Nd memory allocator 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In stdlib.h 42.Ft void * 43.Fn alloca "size_t size" 44.Sh DESCRIPTION 45The 46.Fn alloca 47function 48allocates 49.Fa size 50bytes of space in the stack frame of the caller. 51This temporary space is automatically freed on 52return. 53.Sh RETURN VALUES 54The 55.Fn alloca 56function returns a pointer to the beginning of the allocated space. 57.Sh SEE ALSO 58.Xr brk 2 , 59.Xr calloc 3 , 60.Xr getpagesize 3 , 61.Xr malloc 3 , 62.Xr realloc 3 63.Sh HISTORY 64The 65.Fn alloca 66function appeared in 67.At 32v . 68.\" .Bx ?? . 69.\" The function appeared in 32v, pwb and pwb.2 and in 3bsd 4bsd 70.\" The first man page (or link to a man page that I can find at the 71.\" moment is 4.3... 72.Sh BUGS 73The 74.Fn alloca 75function 76is machine and compiler dependent; 77its use is discouraged. 78.Pp 79The 80.Fn alloca 81function is slightly unsafe because it cannot ensure that the pointer 82returned points to a valid and usable block of memory. 83The allocation made may exceed the bounds of the stack, or even go 84further into other objects in memory, and 85.Fn alloca 86cannot determine such an error. 87Avoid 88.Fn alloca 89with large unbounded allocations. 90