What do brk and sbrk do?

[FinalBirdman]

What do the functions brk and sbrk do in C? I need to allocate more core memory, and I need some good information on how these functions work.

Thanks.

 

[chipperMDW]

man brk

 

[FinalBirdman]

Not sure what you mean...

 

[chipperMDW]

man is short for "manual." It's a UNIX command that brings up a help page on the given topic.

 

[chipperMDW]

I had assumed you were using some form of UNIX since you're using brk and sbrk, but since you're unfamiliar with "man," I guess you might not be. If it helps, here's the man page I get for brk:

NAME
       brk, sbrk − change data segment size

SYNOPSIS
       #include <unistd.h>

       int brk(void *end_data_segment);

       void *sbrk(ptrdiff_t increment);

DESCRIPTION
brk  sets  the  end  of  the  data  segment  to  the value specified by end_data_segment, when that value is reasonable, the system  does  have enough  memory  and  the process does not exceed its max data size (see setrlimit(2)).

sbrk increments the program’s data  space  by  increment  bytes.   sbrk isn’t a system call, it is just a C library wrapper.  Calling sbrk with an increment of 0 can be used to find the current location of the  program break.

RETURN VALUE
On  success,  brk returns zero, and sbrk returns a pointer to the start of the new area.  On error, &#8722;1 is returned, and errno is set to ENOMEM.

CONFORMING TO
BSD 4.3

brk  and  sbrk  are  not defined in the C Standard and are deliberately excluded from  the  POSIX.1  standard  (see  paragraphs  B.1.1.1.3  and B.8.3.3).

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

 

[FinalBirdman]

Thanks!

Yeah, I'm using dos 6.22, not unix. Guess I should have mentioned that. Thanks for the information.