change the location of the
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.
sets the end of the data segment to the value specified by
when that value is reasonable, the system has enough memory,
and the process does not exceed its maximum data size (see
increments the program's data space by
of 0 can be used to find the current location of the program break.
On error, -1 is returned, and
is set to
(But see Linux Notes below.)
returns the previous program break.
(If the break was increased,
then this value is a pointer to the start of the newly allocated memory).
(void *) -1
is returned, and
is set to
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
memory allocation package is the
portable and comfortable way of allocating memory.
Various systems use various types for the argument of
Common are int, ssize_t, ptrdiff_t, intptr_t.
The return value described above for
is the behavior provided by the glibc wrapper function for the Linux
(On most other implementations, the return value from
is the same; this return value was also specified in SUSv2.)
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
to provide the 0 and -1 return values described above.
is implemented as a library function that uses the
system call, and does some internal bookkeeping so that it can
return the old break value.