BRK(2)              UNIX Programmer's Manual               BRK(2)

NAME
     brk, sbrk, break - change core allocation

SYNOPSIS
     char *brk(addr)

     char *sbrk(incr)

DESCRIPTION
     _B_r_k sets the system's idea of the lowest location not used
     by the program (called the break) to _a_d_d_r (rounded up to the
     next multiple of 64 bytes on the PDP-11, 256 bytes on the
     Interdata 8/32, 512 bytes on the VAX-11).  Locations not
     less than _a_d_d_r and below the stack pointer are not in the
     address space and will thus cause a memory violation if
     accessed.

     In the alternate function _s_b_r_k, _i_n_c_r 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 _e_x_e_c_v_e 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 _b_r_e_a_k.

RETURN VALUE
     Zero is returned if the break could be set; -1 if the pro-
     gram requests more memory than the system limit or if too
     many segmentation registers would be required to implement
     the break.

ERRORS
     _S_b_r_k will fail and no additional memory will be allocated
     if:

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

     [ENOMEM]            The maximum available memory for a user
                         process was exceeded.

SEE ALSO
     execve(2), end(3), malloc(3)

BUGS
     Setting the break in the range 0177701 to 0177777 (on the
     PDP-11) is the same as setting it to zero.

ASSEMBLER
     (break = 17.)

Printed 5/26/83                                                 1

BRK(2)              UNIX Programmer's Manual               BRK(2)

     sys break; addr

     _B_r_e_a_k performs the function of _b_r_k.  The name of the routine
     differs from that in C for historical reasons.

Printed 5/26/83                                                 2