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.\" 3. 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.\" 31.Dd March 1, 2019 32.Dt ALLOCA 3 33.Os 34.Sh NAME 35.Nm alloca 36.Nd memory allocator 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In stdlib.h 41.Ft void * 42.Fn alloca "size_t size" 43.Sh DESCRIPTION 44The 45.Fn alloca 46function 47allocates 48.Fa size 49bytes of space in the stack frame of the caller. 50This temporary space is automatically freed on 51return. 52.Sh RETURN VALUES 53The 54.Fn alloca 55function returns a pointer to the beginning of the allocated space. 56.Sh SEE ALSO 57.Xr calloc 3 , 58.Xr getpagesize 3 , 59.Xr malloc 3 , 60.Xr realloc 3 61.Sh HISTORY 62The 63.Fn alloca 64function 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 71The 72.Fn alloca 73function 74is machine and compiler dependent; 75its use is discouraged. 76.Pp 77The 78.Fn alloca 79function is slightly unsafe because it cannot ensure that the pointer 80returned points to a valid and usable block of memory. 81The allocation made may exceed the bounds of the stack, or even go 82further into other objects in memory, and 83.Fn alloca 84cannot determine such an error. 85Avoid 86.Fn alloca 87with large unbounded allocations. 88