GNU Info

(libc.info)Resizing the Data Segment

---

Prev: Locking Pages Up: Memory

---

Enter node , (file) or (file)node

Resizing the Data Segment
=========================

   The symbols in this section are declared in `unistd.h'.

   You will not normally use the functions in this section, because the
functions described in Note: Memory Allocation are easier to use.
Those are interfaces to a GNU C Library memory allocator that uses the
functions below itself.  The functions below are simple interfaces to
system calls.

 - Function: int brk (void *ADDR)
     `brk' sets the high end of the calling process' data segment to
     ADDR.

     The address of the end of a segment is defined to be the address
     of the last byte in the segment plus 1.

     The function has no effect if ADDR is lower than the low end of
     the data segment.  (This is considered success, by the way).

     The function fails if it would cause the data segment to overlap
     another segment or exceed the process' data storage limit (Note:
     Limits on Resources).

     The function is named for a common historical case where data
     storage and the stack are in the same segment.  Data storage
     allocation grows upward from the bottom of the segment while the
     stack grows downward toward it from the top of the segment and the
     curtain between them is called the "break".

     The return value is zero on success.  On failure, the return value
     is `-1' and `errno' is set accordingly.  The following `errno'
     values are specific to this function:

    `ENOMEM'
          The request would cause the data segment to overlap another
          segment or exceed the process' data storage limit.


 - Function: int sbrk (ptrdiff_t DELTA)
     This function is the same as `brk' except that you specify the new
     end of the data segment as an offset DELTA from the current end
     and on success the return value is the address of the resulting
     end of the data segment instead of zero.

     This means you can use `sbrk(0)' to find out what the current end
     of the data segment is.