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 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 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  speci-
       fied  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 3.25 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)