Prevent DLL causing segmenataion fault

[mjaggard]

I have a DLL that I need to call. It's written in Pascal and although I have the source, I don't have pascal so I'm stuck with using the compiled DLL. The problem I have is that when I call a function, it seems to be using the pointer and then changing MY memory - and not just the variable I passed it, other variables nearby. So when I am in the middle of doing something else (normally writing debug), my data is changing.

My question is, is there any way to prevent the DLL from doing this? I tried adding a buffer zone between the memory I pass it and the memory I use.

void MyClass::myFunction(int myParameter)
{
  int myVariable;
  int myOtherVariable = myParameter * 2;

  int ignore[10000];
  ignore[0] = 0; //Just to stop compiler warning about unused variable!

  int variableToPass = 40;
  int otherVariableToPass;

  for (myVariable = 0; myVariable < myOtherVariable; myVariable++)
  {
    otherVariableToPass = 0 + myVariable;
    CallNaughtyDLL(variableToPass, otherVariableToPass);
    qDebug("Print some nice debug %d", myVariable);
  }
}

However this just results in a Segmentation Fault at the end of the function on the line with the last }. I guess because the naughty DLL is still using the memory?

[Duthomhas]

It would help quite a bit more if we could see the exact code in question, and possibly the Pascal code for the DLL or a link to where we can get it online.

[mjaggard]

The code is on the following website. Listed as DLL Source Code.

[mjaggard]

http://www.velleman.eu/distributor/support/downloads/?code=K8062

[Duthomhas]

Sorry, I keep getting sent to the 'Locale' page, which asks me for my country and language.

[mjaggard]

How odd. I'm in the UK and have no problem on that page. I have however found a forum where they talk about products made by velleman and doing a search revealed a new version of the DLL which although still has the problem, also gives another method. Using this new method, I can just use all my data to build an array and send it all at once, so the call is no longer inside a loop. This seems to mean that segmentation fault crashes don't happen (though more by luck than judgement I think).

What I'm saying I guess is that I've resolved my problem for now but I'd still like to know (and might be useful to others) if / how you can get around a buggy DLL crashing your program.

Thanks,
Mat.