brk(2)								System Calls Manual							    brk(2)

NAME

       brk, sbrk - change data segment space allocation

SYNOPSIS

DESCRIPTION

       and  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  loca-
       tion  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.

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

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

ERRORS

       and 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.

       [EINVAL]       Such a change will result in crossing the boundary to uninitialized data in the calling process's data segment.

WARNINGS

       The pointer returned by is not necessarily word-aligned.  Loading or storing words through this pointer could cause  word  alignment  prob-
       lems.

       Be  very careful when using either or 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.

RETURN VALUE

       Upon successful completion, returns a value of 0. Otherwise, a value of -1 is returned and is set to indicate the error.

       Upon successful completion, returns the old break value. Otherwise, is returned and is set to indicate the error. The symbol is defined	in
       the header No successful return from will return the value

AUTHOR

       and were developed by AT&T and HP.

SEE ALSO

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

STANDARDS CONFORMANCE

																	    brk(2)