brk, sbrk — change data segment size
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.
zero. On error, −1 is returned, and
errno is set to ENOMEM.
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.
sbrk(): the malloc(3) memory allocation
package is the portable and comfortable way of allocating
Various systems use various types for the argument of
sbrk(). Common are int, ssize_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.
implemented as a library function that uses the
brk() system call, and does
some internal bookkeeping so that it can return the old
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Copyright (c) 1993 Michael Haardt
Fri Apr 2 11:32:09 MET DST 1993
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.
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but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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Modified Wed Jul 21 19:52:58 1993 by Rik Faith <faithcs.unc.edu>
Modified Sun Aug 21 17:40:38 1994 by Rik Faith <faithcs.unc.edu>