ldd.1, sprof.1, accept.2, alarm.2, bind.2, chdir.2, clock_nanosleep.2, close.2, conne...

[thirdparty/man-pages.git] / man3 / malloc.3

.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified Sat Jul 24 19:00:59 1993 by Rik Faith (faith@cs.unc.edu)
.\" Clarification concerning realloc, iwj10@cus.cam.ac.uk (Ian Jackson), 950701
.\" Documented MALLOC_CHECK_, Wolfram Gloger (wmglo@dent.med.uni-muenchen.de)
.\" 2007-09-15 mtk: added notes on malloc()'s use of sbrk() and mmap().
.\"
.\" FIXME . Review http://austingroupbugs.net/view.php?id=374
.\" to see what changes are required on this page.
.\"
.TH MALLOC 3  2015-08-08 "GNU" "Linux Programmer's Manual"
.SH NAME
malloc, free, calloc, realloc \- allocate and free dynamic memory
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.sp
.BI "void *malloc(size_t " "size" );
.BI "void free(void " "*ptr" );
.BI "void *calloc(size_t " "nmemb" ", size_t " "size" );
.BI "void *realloc(void " "*ptr" ", size_t "  "size" );
.fi
.SH DESCRIPTION
.PP
The
.BR malloc ()
function allocates
.I size
bytes and returns a pointer to the allocated memory.
.IR "The memory is not initialized" .
If
.I size
is 0, then
.BR malloc ()
returns either NULL,
.\" glibc does this:
or a unique pointer value that can later be successfully passed to
.BR free ().
.PP
The
.BR free ()
function frees the memory space pointed to by
.IR ptr ,
which must have been returned by a previous call to
.BR malloc (),
.BR calloc (),
or
.BR realloc ().
Otherwise, or if
.I free(ptr)
has already been called before, undefined behavior occurs.
If
.I ptr
is NULL, no operation is performed.
.PP
The
.BR calloc ()
function allocates memory for an array of
.I nmemb
elements of
.I size
bytes each and returns a pointer to the allocated memory.
The memory is set to zero.
If
.I nmemb
or
.I size
is 0, then
.BR calloc ()
returns either NULL,
.\" glibc does this:
or a unique pointer value that can later be successfully passed to
.BR free ().
.PP
The
.BR realloc ()
function changes the size of the memory block pointed to by
.I ptr
to
.I size
bytes.
The contents will be unchanged in the range from the start of the region
up to the minimum of the old and new sizes.
If the new size is larger than the old size, the added memory will
.I not
be initialized.
If
.I ptr
is NULL, then the call is equivalent to
.IR malloc(size) ,
for all values of
.IR size ;
if
.I size
is equal to zero,
and
.I ptr
is not NULL, then the call is equivalent to
.IR free(ptr) .
Unless
.I ptr
is NULL, it must have been returned by an earlier call to
.BR malloc (),
.BR calloc ()
or
.BR realloc ().
If the area pointed to was moved, a
.I free(ptr)
is done.
.SH RETURN VALUE
The
.BR malloc ()
and
.BR calloc ()
functions return a pointer to the allocated memory,
which is suitably aligned for any built-in type.
On error, these functions return NULL.
NULL may also be returned by a successful call to
.BR malloc ()
with a
.I size
of zero,
or by a successful call to