BRK(S) UNIX System V BRK(S)
Name
brk, sbrk - change data segment space allocation
Syntax
int brk (endds)
char *endds;
char *sbrk (incr)
int incr;
Description
The brk and sbrk system calls are used to change dynamically
the amount of space allocated for the calling process's data
segment (see exec(S)). The change is made by resetting the
process's break value and allocating the appropriate amount
of space. The break value is the address of the first
location beyond the end of the data segment. The amount of
allocated space increases as the break value increases.
Newly allocated space is set to zero. If, however, the same
memory space is reallocated to the same process, its
contents are undefined.
The brk system call sets the break value to endds and
changes the allocated space accordingly.
The sbrk system call adds incr bytes to the break value and
changes the allocated space accordingly. incr can be
negative, in which case the amount of allocated space is
decreased.
The brk and sbrk system calls will fail without making any
change in the allocated space if one or more of the
following is true:
[ENOMEM] Such a change would result in more space
being allocated than is allowed by the
system-imposed maximum process size (see
ulimit(S)).
[EAGAIN] Total amount of system memory available
for a read during physical IO is
temporarily insufficient (see shmop(S)).
This may occur even though the space
requested was less than the system-imposed
maximum process size (see ulimit(S)).
Return Value
Upon successful completion brk returns a value of 0, and
sbrk returns the old break value. Otherwise, a value of -1
is returned and errno is set to indicate the error.
See Also
exec(S), shmop(S), ulimit(S), end(S).
Standards Conformance
brk and sbrk are conformant with:
The X/Open Portability Guide II of January 1987.
(printed 6/20/89)