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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  mem-
       ory.

       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.  (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  mem-
       ory).  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  information   about   reporting   bugs,   can   be   found   at
       http://www.kernel.org/doc/man-pages/.



Linux                             2008-06-18                            BRK(2)

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