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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():
           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
       This page is part of release 3.53 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                                       2010-09-20                                     BRK(2)

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