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():
           Since glibc 2.12:
               _BSD_SOURCE || _SVID_SOURCE ||
                   (_XOPEN_SOURCE >= 500 ||
                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
                   !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
           Before glibc 2.12:
               _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
               _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

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 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.

RETURN VALUE

       On success, brk() returns zero.  On error, -1 is returned, and errno is set to ENOMEM.

       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.

   C library/kernel differences
       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 4.04 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.