Mail Archives: djgpp/1997/07/17/05:18:17
Joshua Eckstein wrote:
>
> I've written a simple program to open a PCX file in mode 0x13, fade it from
> black, rotate it's palette 256 times, and fade out. I have a problem
> because in DOS, it bombs with a traceback once I get to the part where it's
> supposed to begin to rotate the palette. In windows, the whole program runs
> fine. What
> 's going on? What does Windows know that DOS and I don't?! Is it the DPMI
> server? The stack? What? Please reply ASAP to kwe1 AT flash DOT net !!!
Most likely, CWSDPMI is detecting that your program attempts to
dereference a NULL pointer and gives a SIGSEGV. Windows' DPMI host does
not detect this sort of thing (it's a feature of DPMI 1.0), so your
program goes merrily along doing what it's not supposed to do. To test
to see if this is the case, initialize the global _crt0_startup_flags
variable with the _CRT0_FLAG_NULLOK flag. If your program now works
under DOS, then it's a NULL pointer problem and must be debugged.
BTW, to find out exactly where your program crashed, use the 'symify'
utility when the crash traceback is still on the screen. This will
report the function, file, and line number where the crash occurred;
it's then up to you to find and fix it. If you want interactive
debugging, use RHGDB, the debugger that accompanies the RHIDE IDE.
> P.S. BTW, what does the stack size, etc., that you can edit in stubedit
> affect?
All automatic variables are allocated from the stack. Since the stack
has a fixed size, you must be careful not to use extremely large
automatic variables, or nest functions too deeply. The default stack is
256K; if you think you need more, use 'stubedit' to enlarge it, or
initialize the global _stklen variable to the desired value in your
program.
Please get the DJGPP Frequently Asked Questions list (v2/faq210b.zip
from SimTel or online at http://www.delorie.com/djgpp/v2faq/), as both
of these are answered there. Your first question is answered in chapter
9.1, and your second in chapter 15.9. Hint: when using the 'info'
reader that comes with DJGPP, you can search the FAQ for a topic by
pressing 's'.
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