Name
brk, sbrk — change data segment size
Synopsis
#include <unistd.h>
int
brk( |
void * |
end_data_segment); |
void
*sbrk( |
intptr_t |
increment); |
DESCRIPTION
brk() sets the end of the
data segment to the value specified by end_data_segment, when that
value is reasonable, the system does have enough memory and
the process does not exceed its max data size (see setrlimit(2)).
sbrk() increments the
program's data space by increment bytes. sbrk() isn't a system call, it is just a C
library wrapper. 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. (But see Linux Notes below.)
On success, sbrk() returns a
pointer to the start of the new area. On error, −1 is
returned, and errno is set to
ENOMEM.
CONFORMING TO
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in
POSIX.1-2001.
brk() and sbrk() are not defined in the C Standard
and are deliberately excluded from the POSIX.1 standard (see
paragraphs B.1.1.1.3 and B.8.3.3).
NOTES
Various systems use various types for the parameter of
sbrk(). Common are int, ssize_t, ptrdiff_t, intptr_t.
Linux Notes
The return value described above for brk() is the behaviour provided by the
glibc wrapper function for the Linux brk() system call. (On most other
implementations, the return value from brk() is the same.) However, the actual
Linux system call returns the new program break on success.
On failure, the system call returns the current break (thus
for example, the call brk(0) can be used to
obtain the current break). The glibc wrapper function does
some work 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.
SEE ALSO
execve(2), getrlimit(2), malloc(3)
Copyright (c) 1993 Michael Haardt
(michael@moria.de),
Fri Apr 2 11:32:09 MET DST 1993
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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
USA.
Modified Wed Jul 21 19:52:58 1993 by Rik Faith <faith@cs.unc.edu>
Modified Sun Aug 21 17:40:38 1994 by Rik Faith <faith@cs.unc.edu>
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