@node brk, memory
@findex brk
@subheading Syntax

@example
#include <unistd.h>

int brk(void *ptr);
@end example

@subheading Description

This function changes the @emph{break} for the program.  This is the
first address that, if referenced, will cause a fault to occur.  The
program asks for more memory by specifying larger values for @var{ptr}. 
Normally, this is done transparently through the @code{malloc} function. 

@subheading Return Value

Zero if the break was changed, -1 if not.  @code{errno} is set to the
error. 

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
if (brk(old_brk+1000))
  printf("no memory\n");
@end example

@c ----------------------------------------------------------------------
@node sbrk, memory
@findex sbrk
@subheading Syntax

@example
#include <unistd.h>

void *sbrk(int delta)
@end example

@subheading Description

This function changes the "break" of the program by adding @var{delta}
to it.  This is the highest address that your program can access without
causing a violation.  Since the heap is the region under the break, you
can expand the heap (where @code{malloc} gets memory from) by increasing
the break. 

This function is normally accessed only by @code{malloc} (@pxref{malloc}).

@subheading Return Value

The address of the first byte outside of the previous valid address
range, or -1 if no more memory could be accessed.  In other words, a
pointer to the chunk of heap you just allocated, if you had passed a
positive number.

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
char *buf;
buf = sbrk(1000); /* allocate space */
@end example

@c ----------------------------------------------------------------------
@node _stklen, startup
@vindex _stklen
@subheading Syntax

@example
extern int _stklen;
@end example

@subheading Description

This variable sets the minimum stack length that the program requires. 
Note that the stack may be much larger than this.  This value should be
set statically, as it is only used at startup. 

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
int _stklen = 256000;
@end example

@c ----------------------------------------------------------------------
@node __djgpp_memory_handle_list, memory
@vindex __djgpp_memory_handle_list
@subheading Syntax

@example
#include <crt0.h>

extern __djgpp_sbrk_handle __djgpp_memory_handle_list[256];
@end example

@subheading Description

This array contains a list of memory handles and program relative offsets
allocated by sbrk() in addition to the handle allocated by the stub.  These 
values are normally not needed unless you are doing low-level DPMI page 
protection or memory mapping.

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
#include <crt0.h>

  for(i=0; i<256; i++) @{
    int h, a, s;
    h = __djgpp_memory_handle_list[i].handle;
    a = __djgpp_memory_handle_list[i].address;
    s = __djgpp_memory_handle_size[i];    
    if(a == 0 && i != 0) break;
    printf("handle[%d]=0x%x base=0x%x size=0x%x\n",i,h,a,s);
  @}
@end example

@c ----------------------------------------------------------------------
@node __djgpp_memory_handle_size, memory
@vindex __djgpp_memory_handle_size
@subheading Syntax

@example
#include <crt0.h>

extern unsigned __djgpp_memory_handle_size[256];
@end example

@subheading Description

This array contains a list of the sizes of the memory regions allocated 
by sbrk() in addition to the memory region allocated by the stub.  These 
values are normally not needed unless you are dumping the memory blocks.

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
#include <crt0.h>

  for(i=0; i<256; i++) @{
    int h, a, s;
    h = __djgpp_memory_handle_list[i].handle;
    a = __djgpp_memory_handle_list[i].address;
    s = __djgpp_memory_handle_size[i];    
    if(a == 0 && i != 0) break;
    printf("handle[%d]=0x%x base=0x%x size=0x%x\n",i,h,a,s);
  @}
@end example

@c ----------------------------------------------------------------------
@node _exit, process
@findex _exit
@subheading Syntax

@example
#include <unistd.h>

void _exit(int exit_code);
@end example

@subheading Description

This function exits the program, returning @var{exit_code} to the
calling process.  No additional processing (such as closing file
descriptors or calls to the static destructor functions) is done, and
any @code{atexit} functions are not called; only the hardware interrupt
handlers are unhooked, to prevent system crashes e.g. after a call to
@code{abort}.  This function is normally called only by @code{exit} and
@code{abort}.

@subheading Return Value

This function does not return.

@subheading Portability

@portability !ansi, !posix

@c ----------------------------------------------------------------------
@node __exit, process
@findex __exit
@subheading Syntax

@example
#include <unistd.h>

void __exit(int exit_code);
@end example

@subheading Description

This is an internal library function which exits the program, returning
@var{exit_code} to the calling process.  No additional processing is
done, and any @code{atexit} functions are not called.  Since hardware
interrupts are not unhooked, this can cause crashes after the program
exits. This function is normally called only by @code{_exit}; do
@emph{not} call it directly.

@subheading Return Value

This function does not return.

@subheading Portability

@portability !ansi, posix