[apple/libc.git] / stdlib / FreeBSD / alloca.3

.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)alloca.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/stdlib/alloca.3,v 1.13 2007/01/09 00:28:09 imp Exp $
.\"
.Dd September 5, 2006
.Dt ALLOCA 3
.Os
.Sh NAME
.Nm alloca
.Nd memory allocator
.Sh SYNOPSIS
.In alloca.h
or
.br
.In stdlib.h
.Ft void *
.Fn alloca "size_t size"
.Sh DESCRIPTION
The
.Fn alloca
macro
allocates
.Fa size
bytes of space in the stack frame of the caller.
This temporary space is automatically freed on
return.
.Sh RETURN VALUES
.Fn alloca
returns a pointer to the beginning of the allocated space.
.Sh SEE ALSO
.Xr brk 2 ,
.Xr calloc 3 ,
.Xr getpagesize 3 ,
.Xr malloc 3 ,
.Xr realloc 3
.Sh HISTORY
.Fn alloca
appeared in
.At 32v .
.\" .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...
.Sh BUGS
.Fn alloca
is machine and compiler dependent;
its use is discouraged.
.Pp
.Fn alloca
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.
.Pp
The use of C99 variable-length arrays and
.Fn alloca
in the same function will cause the lifetime of alloca's storage to be limited to the block containing the
.Fn alloca
Commit	Line	Data
5b2abdfb	1	.\" Copyright (c) 1980, 1991, 1993
e9ce8d39 A	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.
e9ce8d39 A	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	.\"
5b2abdfb	28	.\" @(#)alloca.3 8.1 (Berkeley) 6/4/93
1f2f436a	29	.\" $FreeBSD: src/lib/libc/stdlib/alloca.3,v 1.13 2007/01/09 00:28:09 imp Exp $
e9ce8d39	30	.\"
1f2f436a	31	.Dd September 5, 2006
5b2abdfb	32	.Dt ALLOCA 3
e9ce8d39 A	33	.Os
e9ce8d39 A	34	.Sh NAME
5b2abdfb A	35	.Nm alloca
5b2abdfb A	36	.Nd memory allocator
e9ce8d39	37	.Sh SYNOPSIS
ad3c9f2a A	38	.In alloca.h
	39	or
	40	.br
5b2abdfb A	41	.In stdlib.h
	42	.Ft void *
	43	.Fn alloca "size_t size"
e9ce8d39 A	44	.Sh DESCRIPTION
e9ce8d39 A	45	The
5b2abdfb	46	.Fn alloca
ad3c9f2a	47	macro
5b2abdfb A	48	allocates
	49	.Fa size
	50	bytes of space in the stack frame of the caller.
	51	This temporary space is automatically freed on
	52	return.
e9ce8d39	53	.Sh RETURN VALUES
5b2abdfb	54	.Fn alloca
ad3c9f2a	55	returns a pointer to the beginning of the allocated space.
e9ce8d39	56	.Sh SEE ALSO
5b2abdfb A	57	.Xr brk 2 ,
	58	.Xr calloc 3 ,
	59	.Xr getpagesize 3 ,
	60	.Xr malloc 3 ,
	61	.Xr realloc 3
3d9156a7	62	.Sh HISTORY
5b2abdfb	63	.Fn alloca
ad3c9f2a	64	appeared in
3d9156a7	65	.At 32v .
5b2abdfb A	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...
3d9156a7	70	.Sh BUGS
3d9156a7	71	.Fn alloca
3d9156a7 A	72	is machine and compiler dependent;
3d9156a7 A	73	its use is discouraged.
1f2f436a	74	.Pp
1f2f436a	75	.Fn alloca
ad3c9f2a	76	is slightly unsafe because it cannot ensure that the pointer
1f2f436a A	77	returned points to a valid and usable block of memory.
	78	The allocation made may exceed the bounds of the stack, or even go
	79	further into other objects in memory, and
	80	.Fn alloca
	81	cannot determine such an error.
	82	Avoid
	83	.Fn alloca
	84	with large unbounded allocations.
ad3c9f2a A	85	.Pp
	86	The use of C99 variable-length arrays and
	87	.Fn alloca
	88	in the same function will cause the lifetime of alloca's storage to be limited to the block containing the
	89	.Fn alloca