brk, sbrk — change data segment size
#include <unistd.h>
int
brk( |
void * | end_data_segment) ; |
void
*sbrk( |
intptr_t | increment) ; |
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.
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.
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).
Various systems use various types for the parameter of
sbrk
(). Common are int
, ssize_t
, ptrdiff_t
, intptr_t
.
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.
execve(2), getrlimit(2), malloc(3)
|