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(): _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. (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 3.23 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 2008-06-18 BRK(2)