Thread: How to detect if a pointer points to invalid memory? (Win32)

The article is correct - if you arbitrarily check ALL kinds of pointers with IsBadXXXPtr then you could cause more problems than you will fix. You should not check stack-addresses with IsBadXXXPtr [1].

Which goes back to Salem's question: What are you actually trying to "fix"? If your app is using some DLL that has a function that returns a pointer to some memory, it is a broken implementation if you can't read that memory. The next question is of course if you and the DLL agree on the size and usage of that memory - but the DLL is fundamentally broken if it doesn't return a valid memory address when that is what's expected of it.

[1] Since the stack is ALWAYS readable and writable by your application, that should cause no problem. The next problem is of course to determine if an address is within the stack. The following code shows how you can do that:

Code:

char *baseStackPtr;
void initStackCheck(void *p)
{
   baseStackPtr = p;
}

int isStackPtr(void *p)
{
    char dummy;
    char *topOfStack = &dummy;
    char *cp = p;
    
    if (cp > baseStackPtr && cp < topOfStack) 
      return 1;
    return 0;
}

int main()
{
    int x;  // Any local variabe in main will do. 
    initStackCheck(&x);
    ....
     // your code goes here.
    
    return 0;
}

Also, you will only hit a stack guardpage if you are using a negative offset off the current stack position, since the stack grows towards zero - so the code is most likely broken in some bad way in the first place, if you hit that problem - because it means you are using some piece of memory that you don't currently own!

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Mats