brk(2)                                                     brk(2)



     NAME
          brk, sbrk - change data segment space allocation

     SYNOPSIS
          int brk(endds)
          char *endds;

          char *sbrk(incr)
          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 al-
          located space accordingly.  incr can be negative, in which
          case the amount of allocated space is decreased.

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

     ERRORS
          brk and sbrk will fail without making any change in the al-
          located space if the following is true:

          [ENOMEM]  Not enough space.  Program asks for more space
                    than the system is able to supply.

          [EAGAIN]  The system has temporarily exhausted its available
                    memory or swap space.

          Such a change would result in more space being allocated
          than is allowed by a system-imposed maximum (see ulimit(2)).
          Such a change would result in the break value being greater
          than or equal to the start address of any attached shared
          memory segment (see shmop(2)).

     SEE ALSO
          exec(2), shmop(2), ulimit(2).





     April, 1990                                                     1