term% cat index.txt BRK(2) System Calls Manual BRK(2)
NAME
brk, sbrk, break - change core allocation
SYNOPSIS
char *brk(addr)
char *sbrk(incr)
DESCRIPTION
Brk sets the system's idea of the lowest location not used by the pro‐
gram (called the break) to addr (rounded up to the next multiple of 64
bytes on a PDP11 and 1024 bytes on a VAX). Locations not less than
addr and below the stack pointer are not in the address space and will
thus cause a memory violation if accessed.
In the alternate function sbrk, incr more bytes are added to the pro‐
gram's data space and a pointer to the start of the new area is re‐
turned. (Rounding occurs as with brk, but a nominal break is remem‐
bered, so rounding does not accumulate.)
When a program begins execution via exec the break is set at the high‐
est location defined by the program and data storage areas. Ordinar‐
ily, therefore, only programs with growing data areas need to use
break.
SEE ALSO
exec(2), malloc(3), end(3)
DIAGNOSTICS
Zero is returned if the brk could be set; -1 if the program requests
more memory than the system limit or if too many segmentation registers
would be required to implement the break. Sbrk returns -1 if the break
could not be set.
BRK(2)