From:	j DOT aldrich6 AT genie DOT com
Message-Id:	<199604260152.AA095763564@relay1.geis.com>
Date:	Fri, 26 Apr 96 01:55:00 UTC 0000
To:	djgpp AT delorie DOT com
Mime-Version:	1.0
Subject:	Re: problem with DJGPP and arr

Reply to message 8372573    from GAGHON AT NEVADA on 04/23/96 11:03PM


>Ok I am having a problem with DJGPP and large arrays.  All my arrays do
>not exceed 2megs of RAM (combined).

There's your problem right there.  Something similarly evil happened to me
not long ago, and it was because DJGPP's default stack size is 256KB, and
your arrays are being allocated WAY beyond the bottom of that stack.

Remember your basic memory organization:

---Top---
    /\
     |
--Heap---  (grows upwards)
--Stack-- (grows downwards)
     |
    \/
--Data--- (static storage)
     |
--Code--- (static storage)
     |
-Bottom-  (OS & other low-level stuff)

If you use more stack space than is allocated, your automatic variables
begin overwriting first your static storage,followed by your code, followed
by low-level memory.  When your program tries to write into this space,
the DPMI host generates a segmentation violation (or a page fault - I'm not
sure which).

BTW, the FAQ's solution tothe problem is wrong (unless the FAQ has
been updated?).  You can certainly stubedit your executable with no
problem, but to increase the stack within your program, you have to
put the following line in your main program file:

unsigned int _stklen = <size>;

Where <size> is the amount of stack you want to allocate.  Do NOT
declare it extern, because you can't declare extern and initialize at
the same time.  However, if you are really using as much storage
space as you seem to be, you'd be much better off simply declaring
the variables as static, so they get allocated in your static data space.

Hope this helps

John

- Raw text -