From: "Andreas Björk" <97andbj AT ostrabo DOT uddevalla DOT se>
Newsgroups: comp.os.msdos.djgpp
Subject: How can i create a working virtual screen i DJGPP?
Date: Fri, 12 Sep 1997 18:14:05 +0200
Organization: Algonet/Tninet
Lines: 61
Message-ID: <34196A4D.1539879@ostrabo.uddevalla.se>
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To: djgpp AT delorie DOT com
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How can i easy create a virtual screens and then flip them to the
VGA memory (0xA0000)?? Is there anyone out there who has
good routines for it??

I have test to this, but i get error messages when i execute the EXE
file.
The file compiles and links as it should.
The error message looks like this:

------------------------------------------------------------------------

Exiting due to signal SIGSEGV
General Protection Fault at eip=000126b9
eax=000a0000 ebx=00060140 ecx=00003e80 edx=0000fa00 esi=00067000
edi=000a0000
ebp=0005e4f8 esp=0005e4ec program=D:\DJGPP\PRJ\GRAF\TEST.EXE
cs: sel=00a7  base=83413000  limit=0008ffff
ds: sel=00af  base=83413000  limit=0008ffff
es: sel=00af  base=83413000  limit=0008ffff
fs: sel=0087  base=000222f0  limit=0000ffff
gs: sel=00c7  base=00000000  limit=ffffffff
ss: sel=00af  base=83413000  limit=0008ffff

Call frame traceback EIPs:
  0x000126b9
  0x0000167d
  0x000016a6
  0x0000e3e6
------------------------------------------------------------------------

parts of my code:

void SetUpVirtual()
{
  unsigned char *ScreenBuf = (unsigned char*) calloc(64000,1);
  if(ScreenBuf == NULL)
  {
    SetMode(0x3);
    cout << "not enough memory available, exiting program..";
    exit(1);
  }
}

void Cls(unsigned char Col,unsigned char *Where)
{
  memset(Where,Col,64000);
}

void Flip()
{
  memcpy(vga,ScreenBuf,64000);
}

-------------------------------------------------------------

When i try to flip the virtual screen to the VGA mem i get the error
message earlier in the document. If i don't use the Flip function the
file executes as it should..  but then i don't work i will.

So can anyone help me please...