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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.  (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

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