NAME
brk, sbrk — change data segment space allocation
SYNOPSIS
#include <unistd.h>
int brk(const void *endds);
void *sbrk(int incr);
DESCRIPTION
brk()
and
sbrk()
are used to change dynamically the amount of space allocated
for the calling process's data segment; see
exec(2).
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.
The newly allocated space is set to zero.
brk()
sets the break value to
endds
and changes the allocated space accordingly.
sbrk()
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.
ERRORS
brk()
and
sbrk()
fail without making any change in the allocated space if one or more of
the following are true:
- [ENOMEM]
Such a change would result in more space being allocated
than is allowed by a system-imposed maximum (see
ulimit(2)).
- [ENOMEM]
Such a change would cause a conflict between addresses in the data
segment and any attached shared memory segment
(see
shmop(2)).
- [ENOMEM]
Such a change would be impossible as there is insufficient swap
space available.
- [EINVAL]
Such a change will result in crossing the boundary to uninitialized
data in the calling process's data segment.
WARNINGS
The pointer returned by
sbrk()
is not necessarily word-aligned.
Loading or storing words through this pointer
could cause word alignment problems.
Be very careful when using either
brk
or
sbrk
in conjunction with calls to the
malloc(3C)
library routines.
There is only one program data segment from which
all three of these routines allocate and deallocate program data memory.
RETURN VALUE
Upon successful completion,
brk()
returns a value of 0. Otherwise, a value of -1 is returned and
errno
is set to indicate the error.
Upon successful completion,
sbrk()
returns the old break value. Otherwise,
SBRK_FAILED
is returned and
errno
is set to indicate the error. The symbol
SBRK_FAILED
is defined in the
header
<unistd.h>.
No successful return from
sbrk()
will return the value
SBRK_FAILED.
AUTHOR
brk()
and
sbrk()
were developed by
AT&T and HP.
STANDARDS CONFORMANCE
brk(): XPG2
sbrk(): XPG2
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