BRK(2)                               BSD                                BRK(2)



NAME
     brk, sbrk - change data segment size

SYNOPSIS
     char *brk(addr)
     char *addr;

     char *sbrk(incr)
     int incr;

DESCRIPTION
     brk sets the system's idea of the lowest data segment location not used
     by the program (called the break) to addr (rounded up to the next
     multiple of the system's page size).  Locations greater 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
     program's data space and a pointer to the start of the new area is
     returned.

     When a program begins execution via execve the break is set at the
     highest location defined by the program and data storage areas.
     Ordinarily, therefore, only programs with growing data areas need to use
     sbrk.

     The getrlimit(2) system call can be used to determine the maximum
     permissible size of the data segment; it will not be possible to set the
     break beyond the rlim_max value returned from a call to getrlimit, for
     example, "etext + rlp->rlim_max." (see end(3) for the definition of
     etext).

ERRORS
     sbrk will fail and no additional memory will be allocated if one of the
     following are true:

     [ENOMEM]   The limit, as set by setrlimit(2), was exceeded.

     [ENOMEM]   The maximum possible size of a data segment (compiled into the
                system) was exceeded.

     [ENOMEM]   Insufficient disk space existed for backing storage to support
                the expansion.

SEE ALSO
     execve(2), getrlimit(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.  sbrk returns -1 if the break could not be
     set.

BUGS
     Setting the break may fail due to a temporary lack of backing storage.
     It is not possible to distinguish this from a failure caused by exceeding
     the maximum size of the data segment without consulting getrlimit.