BREAK(II) 8/5/73 BREAK(II)





BREAK(II)                    8/5/73                     BREAK(II)







NAME

     break, brk, sbrk - change core allocation



SYNOPSIS

     (break = 17.)

     sys break; addr



     char *brk(addr)



     char *sbrk(incr)



DESCRIPTION

     Break sets the system's idea of the lowest location not used

     by the program (called the break) to addr (rounded up to the

     next multiple of 64 bytes).  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.



     From C, brk will set the break to addr.  The  old  break  is

     returned.



     In the alternate entry 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 exec 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 break.



SEE ALSO

     exec (II), alloc (III), end (III)



DIAGNOSTICS

     The c-bit is set if the program requests  more  memory  than

     the  system  limit  or if more than 8 segmentation registers

     would be required to implement the break.   From  C,  -1  is

     returned for these errors.



BUGS

     Setting the break in the range 0177700  to  0177777  is  the

     same as setting it to zero.
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