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) for information about transforming processes.  The
     process's break value is reset and the appropriate amount of
     space is allocated.  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.

     (Note that the break value cannot be set to a value less
     than its initial value.)

     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.

STATUS MESSAGES AND VALUES
     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.

     The brk and sbrk programs will fail without making any
     change in the allocated space if any of the following
     conditions is true:

     EINVAL
          The new break value would be less than the original
          value.

     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.





January 1992                                                    1

brk(2)                                                     brk(2)



     Such a change would result in the allocation of more space
     than is allowed by a system-imposed maximum (see ulimit(2)).
     Such a change would result in the break value's 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)















































2                                                    January 1992