Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
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  de-
       fines 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 ABI	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 3.74 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
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-08-19				BRK(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=brk&sektion=2&manpath=Debian+8.1.0>

home | help