Date:	Sun, 23 Nov 1997 18:28:36 -0800 (PST)
Message-Id:	<199711240228.SAA02753@adit.ap.net>
Mime-Version:	1.0
To:	eggbrains AT aol DOT com (Egg brains), djgpp AT delorie DOT com
From:	Nate Eldredge <eldredge AT ap DOT net>
Subject:	Re: computer freezes when i try to get a mouse event using
	0x33 ax=0c

At 12:05  11/22/1997 GMT, Egg brains wrote:
>okay, a few days ago i posted a message here.  i got all the answers i needed
>(thanks) and no errors were genertated while it was compiling (so far so good)
>then when i ran it and clicked my left mouse button (the event I am trying to
>trap)... it generated and annoying win95 error and quit.  i tried running it in
>dos and it froze all thogether. 
>
>i think this is because i am setting a bad vector so that the mouse calls a bad
>reference on the event.... am i right? and does anyone know why this is
>occuring?
Close. See two comments below.
>
>
>---- CODE SNIPPET ----
>
>#include <iostream.h>
>#include <dpmi.h>
>#include <go32.h>
>static __dpmi_regs callback_regs;
>static _go32_dpmi_seginfo callback_info;
>
>void happySub(__dpmi_regs *)
>{
> cout << "abc!!!";
You CANNOT call libc/libstdc++ functions that might call DOS from a hardware
interrupt handler, because DOS is not reentrant. If the user clicked the
mouse while a DOS function was executing, the effects could be disastrous.
Use something that doesn't call DOS, perhaps `cprintf'.
> return;
>}
>
>long initMouse(unsigned mask, void (*func)(__dpmi_regs *))
>{
>  __dpmi_regs r;
>
>  callback_info.pm_offset = (long)func;
>  if
>(_go32_dpmi_allocate_real_mode_callback_retf(&callback_info,&callback_regs))
>    return -1;  /* failure */
>
>  r.x.ax = 0xC;
>  r.x.cx = mask;
You need to tell the mouse driver the address of your handler. It doesn't
know it by magic. :) Add these lines:
r.x.es = callback_info.rm_segment;
r.x.dx = callback_info.rm_offset;
>  __dpmi_int (0x33, &r);
>
>  return (r.x.flags & 1) ? -1 : 0;
>}
>
>void main()
>{
>  char *dummy;
>  cout << "mouse demo";
>  initMouse(0x01, happySub);
>  
>  for(long i; i>0; i++){
>    cout << i << endl;
>  }
>
>  cin >> dummy;
>}
>----END CODE SNIPPET----
Hope this helps.

Nate Eldredge
eldredge AT ap DOT net

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