BRK(2-SysV)         RISC/os Reference Manual          BRK(2-SysV)



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.  Newly allocated
     space is set to zero.  If, however, the same memory space is
     reallocated to the same process its contents are undefined.

     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.

     brk and sbrk will 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 the
                         system-imposed maximum process size [see
                         ulimit(2)].

     [EAGAIN]            Total amount of system memory available
                         for a read during physical IO is tem-
                         porarily insufficient [see shmop(2)].
                         This may occur even though the space
                         requested was less than the system-
                         imposed maximum process size [see
                         ulimit(2)].

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

DIAGNOSTICS
     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.




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