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 brk(2)								      brk(2)




 NAME
      brk, sbrk - change data segment space allocation

 SYNOPSIS
      #include <&lt&lt&lt;unistd.h>&gt&gt&gt;

      int brk(const void *endds);

      void *sbrk(int incr);

 DESCRIPTION
      brk() and sbrk() are used to change dynamically the amount of space
      allocated for the calling process's data segment; see exec(2).  The
      change is made by resetting the process's break value and allocating
      the appropriate amount of space.	The break value is the address of
      the first location beyond the end of the data segment.  The amount of
      allocated space increases as the break value increases.  The newly
      allocated space is set to zero.

      brk() sets the break value to endds and changes the allocated space
      accordingly.

      sbrk() adds incr bytes to the break value and changes the allocated
      space accordingly.  incr can be negative, in which case the amount of
      allocated space is decreased.

 ERRORS
      brk() and sbrk() fail without making any change in the allocated space
      if one or more of the following are true:

      [ENOMEM]	     Such a change would result in more space being
		     allocated than is allowed by a system-imposed maximum
		     (see ulimit(2)).

      [ENOMEM]	     Such a change would cause a conflict between addresses
		     in the data segment and any attached shared memory
		     segment (see shmop(2)).

      [ENOMEM]	     Such a change would be impossible as there is
		     insufficient swap space available.

 WARNINGS
      The pointer returned by sbrk() is not necessarily word-aligned.
      Loading or storing words through this pointer could cause word
      alignment problems.

      Be very careful when using either brk or sbrk in conjunction with
      calls to the malloc(3C) library routines.	 There is only one program
      data segment from which all three of these routines allocate and
      deallocate program data memory.




 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000






 brk(2)								      brk(2)




 RETURN VALUE
      Upon successful completion, brk() returns a value of 0. Otherwise, a
      value of -1 is returned and errno is set to indicate the error.

      Upon successful completion, sbrk() returns the old break value.
      Otherwise, SBRK_FAILED is returned and errno is set to indicate the
      error. The symbol SBRK_FAILED is defined in the header <unistd.h>.  No
      successful return from sbrk() will return the value SBRK_FAILED.

 AUTHOR
      brk() and sbrk() were developed by AT&T and HP.

 SEE ALSO
      exec(2), shmop(2), ulimit(2), end(3C), malloc(3C).

 STANDARDS CONFORMANCE
      brk(): XPG2

      sbrk(): XPG2



































 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000