sbrk

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():
           Since glibc 2.19:
               _DEFAULT_SOURCE ||
                   (_XOPEN_SOURCE >= 500) &&
                   ! (_POSIX_C_SOURCE >= 200112L)
           From glibc 2.12 to 2.19:
               _BSD_SOURCE || _SVID_SOURCE ||
                   (_XOPEN_SOURCE >= 500) &&
                   ! (_POSIX_C_SOURCE >= 200112L)
           Before glibc 2.12:
               _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.

       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 5.03 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
       https://www.kernel.org/doc/man-pages/.




Linux                             2016-03-15                            BRK(2)