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BRK(2)                     Linux Programmer's Manual                    BRK(2)



NAME
       brk, sbrk - change data segment size

SYNOPSIS
       #include <unistd.h>

       int brk(void *addr);

       void *sbrk(intptr_t increment);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       brk(), sbrk(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION
       brk()  and 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  sys-
       tem 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.

RETURN VALUE
       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  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.

CONFORMING TO
       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.

NOTES
       Avoid  using  brk()  and sbrk(): the malloc(3) memory allocation package is the portable and comfortable way of
       allocating memory.

       Various systems use various types for the argument of sbrk().  Common are int, ssize_t, ptrdiff_t, intptr_t.

   Linux Notes
       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.

       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.

SEE ALSO
       execve(2), getrlimit(2), end(3), malloc(3)

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-18                            BRK(2)