| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
BRK(2) Linux Programmer's Manual BRK(2)
brk, sbrk - change data segment size
#include <unistd.h>
int brk(void *addr);
void *sbrk(intptr_t increment);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
brk(), sbrk():
Since glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE ||
(_XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
!(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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.
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 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.
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
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.
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.
execve(2), getrlimit(2), end(3), malloc(3)
This page is part of release 3.41 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-20 BRK(2)
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The Linux Programming Interface,
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