Name
brk, sbrk — change data segment size
Synopsis
#include <unistd.h>
int
brk( |
void *addr); |
void
*sbrk( |
intptr_t increment); |
![[Note]](../stylesheet/note.png) |
Note | |||||||
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DESCRIPTION
brk() and sbrk() change the location of the
program break, which
defines the end of the process's data segment (i.e., the
program break is the first location after the end of the
uninitialized data segment). Increasing the program break has
the effect of allocating memory to the process; decreasing
the break deallocates memory.
brk() sets the end of the
data segment to the value specified by addr, when that value is
reasonable, the system has enough memory, and the process
does not exceed its maximum data size (see setrlimit(2)).
sbrk() increments the
program's data space by increment bytes. Calling
sbrk() with an increment of 0 can be used to
find the current location of the program break.
RETURN VALUE
On success, brk() returns
zero. On error, −1 is returned, and errno is set to ENOMEM.
On success, sbrk() returns
the previous program break. (If the break was increased, then
this value is a pointer to the start of the newly allocated
memory). On error, (void *)
−1 is returned, and errno is set to ENOMEM.
NOTES
Avoid using brk() and
sbrk(): the malloc(3) memory allocation
package is the portable and comfortable way of allocating
memory.
Various systems use various types for the argument of
sbrk(). Common are int, ssize_t,
ptrdiff_t, intptr_t.
C library/kernel differences
The return value described above for brk() is the behavior provided by the
glibc wrapper function for the Linux brk() system call. (On most other
implementations, the return value from brk() is the same; this return value was
also specified in SUSv2.) However, the actual Linux system
call returns the new program break on success. On failure,
the system call returns the current break. The glibc
wrapper function does some work (i.e., checks whether the
new break is less than addr) to provide the 0 and
−1 return values described above.
On Linux, sbrk() is
implemented as a library function that uses the
brk() system call, and does
some internal bookkeeping so that it can return the old
break value.
COLOPHON
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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Copyright (c) 1993 Michael Haardt (michaelmoria.de), Fri Apr 2 11:32:09 MET DST 1993 %%%LICENSE_START(GPLv2+_DOC_FULL) This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END Modified Wed Jul 21 19:52:58 1993 by Rik Faith <faithcs.unc.edu> Modified Sun Aug 21 17:40:38 1994 by Rik Faith <faithcs.unc.edu> |