Question

I’m getting some odd, unexplained errors and crashes in my program. I’ve been stepping through debugging and looking around, and I noticed that I’m setting a variable to NULL, but if I set a breakpoint immediately after, the variable is set to 0xcdcdcd00 even though I just set it to NULL.

It looks like there is some sort of memory corruption happening in my program.

What are some good techniques for finding the cause of the memory corruption? I added a large chunk of code before this started happening, so while going through my code, what are something I should be looking for that can cause memory corruption?

I have a class called monster, derived from a class called mob

I execute the following code:

monster* newMon = new monster();

which calls the constructor on monster class:

monster::monster() : mob() {
    this->renderer = NULL;
}

when I break at the end of this function, renderer = 0xcdcdcd00 or sometimes 0xcdcdcdcd

Answer 1

This

monster::monster() : mob() {
    this->renderer = NULL;
}

sets renderer to NULL. I’d change it to

monster::monster() : mob(), renderer(NULL) {
}

but that shouldn’t make a difference (other than readability).

The problems is one of two things:

• out of date build
• running with optimizations and checking the value in the debugger (this is my guess). It might tell you that renderer is not NULL, but you shouldn’t trust the debugger in a release build.

I’m sure that if you output some debug statements, you’ll see that the value is actually set correctly:

monster::monster() : mob(), renderer(NULL) {
   if (renderer)
       std::cout << "WTH!";
   else
       std::cout << "correctly set to NULL";
}