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.Dd April 29, 2025 29.Dt ALLOCA 3 30.Os 31.Sh NAME 32.Nm alloca 33.Nd memory allocator 34.Sh SYNOPSIS 35.In stdlib.h 36.Ft void * 37.Fn alloca "size_t size" 38.Sh DESCRIPTION 39The 40.Fn alloca 41function 42allocates 43.Fa size 44bytes of space in the stack frame of the caller. 45This temporary space is automatically freed on 46return. 47.Sh RETURN VALUES 48The 49.Fn alloca 50function returns a pointer to the beginning of the allocated space. 51.Sh SEE ALSO 52.Xr brk 2 , 53.Xr calloc 3 , 54.Xr getpagesize 3 , 55.Xr malloc 3 , 56.Xr realloc 3 57.Sh HISTORY 58The 59.Fn alloca 60function appeared in 61.At 32v . 62.\" .Bx ?? . 63.\" The function appeared in 32v, pwb and pwb.2 and in 3bsd 4bsd 64.\" The first man page (or link to a man page that I can find at the 65.\" moment is 4.3... 66.Sh BUGS 67The 68.Fn alloca 69function 70is machine and compiler dependent; 71its use is discouraged. 72.Pp 73The 74.Fn alloca 75function is slightly unsafe because it cannot ensure that the pointer 76returned points to a valid and usable block of memory. 77The allocation made may exceed the bounds of the stack, or even go 78further into other objects in memory, and 79.Fn alloca 80cannot determine such an error. 81Avoid 82.Fn alloca 83with large unbounded allocations. 84