From:	random AT visi DOT net (Michael Bosley)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Q: Please tell me why this is crashing...
Date:	Mon, 04 May 1998 21:02:44 GMT
Organization:	@Home Network
Lines:	88
Message-ID:	<354e2a93.27671024@news>
NNTP-Posting-Host:	cx582964-a.nwptn1.va.home.com
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi all,

I have been trying to do this for (it seems like forever now) a couple
days.  Trace here, trace there... take a break, get a new view of
it... kick the computer :)

I don't know how to read the error info created by a GPF so I need
some help... I have included the error and some of the code below and
I can't quite figure why it is crashing.

Just so you know what I am doing, I am trying to read a PCX file.
It's probably something stupid, I just can't see it anywhere :(  If it
is needed, the machine is a P233 MMX running win95.  If you need any
more info, email me at random AT NOSPAM DOT visi DOT net (remove the NOSPAM.)

Thanks all!!!

Michael Bosley

The Error:

Exiting due to signal SIGSEGV
General Protection Fault at eip=00002d08
eax=0006a000 ebx=0000fa01 ecx=4c4c4f43 edx=00000000 esi=0006a000
edi=0000f9ff
ebp=000623a4 esp=000623a0 program=E:\CPPPROJ\TRIBUTE\UTILS\GFX.EXE
cs: sel=00a7  base=82eaa000  limit=0008ffff
ds: sel=00af  base=82eaa000  limit=0008ffff
es: sel=00af  base=82eaa000  limit=0008ffff
fs: sel=0087  base=0000cf40  limit=0000ffff
gs: sel=00c7  base=00000000  limit=ffffffff
ss: sel=00af  base=82eaa000  limit=0008ffff

Call frame traceback EIPs:
  0x00002d08
  0x000025a5
  0x000030c9
  0x0001213e

...
    typedef struct _RGB_Color {
      int red;
      int green;
      int blue;
    } RGB_Color, *RGB_Color_ptr;
...

    RGB_Color_ptr palette[256 + 1];
/*
  also tried:
    RGB_Color *palette[256 + 1]
    RGB_Color_ptr palette = new RGB_Color_ptr[256+1]
*/
...
  // set the palette information
  // NOTE this _works_ if the for loop does not go past 1 but
  // crashes otherwise...
    for (int index = 0; index < 256; index++) {

      fp.read(&data, 1);
      SetPalette(index, GFX::red,   (data >> 2));

      fp.read(&data, 1);
      SetPalette(index, GFX::green, (data >> 2));

      fp.read(&data, 1);
      SetPalette(index, GFX::blue,  (data >> 2));
    }
...

void GFX::SetPalette(int element, int rgb, unsigned char color) {
  if (rgb == red){
    palette[element]->red   = color;
  } else if (rgb == green) {
    palette[element]->green = color;
  } else {
    palette[element]->blue  = color;
  }
} // end SetPalette






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