brk(2) [bsd man page]

BRK(2)								System Calls Manual							    BRK(2)

NAME

       brk, sbrk - change data segment size

SYNOPSIS

       #include <sys/types.h>

       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.   Ordi-
       narily, therefore, only programs with growing data areas need to use sbrk.

       The  getrlimit(2) system call may 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, e.g. "etext + rlp->rlim_max."  (see end(3) for the definition of etext).

RETURN VALUE

       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.

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 space existed in the swap area to support the expansion.

SEE ALSO

       execve(2), getrlimit(2), malloc(3), end(3)

BUGS

       Setting	the break may fail due to a temporary lack of swap space.  It is not possible to distinguish this from a failure caused by exceed-
       ing the maximum size of the data segment without consulting getrlimit.

4th Berkeley Distribution					   May 22, 1986 							    BRK(2)

BRK(2)							      BSD System Calls Manual							    BRK(2)

NAME

     brk, sbrk -- change data segment size

SYNOPSIS

     #include <unistd.h>

     void *
     brk(const void *addr);

     void *
     sbrk(int incr);

DESCRIPTION

     The brk and sbrk functions are historical curiosities left over from earlier days before the advent of virtual memory management.	The brk()
     function sets the break or lowest address of a process's data segment (uninitialized data) to addr (immediately above bss).  Data addressing
     is restricted between addr and the lowest stack pointer to the stack segment.  Memory is allocated by brk in page size pieces; if addr is not
     evenly divisible by the system page size, it is increased to the next page boundary.

     The current value of the program break is reliably returned by ``sbrk(0)'' (see also end(3)).  The getrlimit(2) system call may 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, e.g.	``qetext + rlp->rlim_max.'' (see end(3) for the definition of etext).

RETURN VALUES

     Brk returns a pointer to the new end of memory if successful; otherwise -1 with errno set to indicate why the allocation failed.  The sbrk
     function returns a pointer to the base of the new storage if successful; otherwise -1 with errno set to indicate why the allocation failed.

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 space existed in the swap area to support the expansion.

SEE ALSO

     execve(2), getrlimit(2), malloc(3), mmap(2), end(3)

BUGS

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

HISTORY

     A brk() function call appeared in Version 7 AT&T UNIX.

4th Berkeley Distribution					 December 11, 1993					 4th Berkeley Distribution