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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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 2.19:
_DEFAULT_SOURCE ||
(_XOPEN_SOURCE >= 500) &&
! (_POSIX_C_SOURCE >= 200112L)
From glibc 2.12 to 2.19:
_BSD_SOURCE || _SVID_SOURCE ||
(_XOPEN_SOURCE >= 500) &&
! (_POSIX_C_SOURCE >= 200112L)
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
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.
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.
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.
execve(2), getrlimit(2), end(3), malloc(3)
This page is part of release 4.12 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/.
Linux 2016-03-15 BRK(2)
Pages that refer to this page: getrlimit(2), mlock(2), mremap(2), prctl(2), shmop(2), syscalls(2), alloca(3), end(3), malloc(3), malloc_hook(3), malloc_trim(3), mallopt(3), posix_memalign(3), proc(5), cpuset(7)