Question

Sorry if this sounds like an “It compiles, so it must work!” question, but I want to understand why something is happening (or not happening, as the case may be).

In Project Settings, I set Basic Runtime Checks to Both. The debugger informs me that:

Run-Time Check Failure #2 – Stack around the variable ‘beg’ was corrupted.

But if I set it to the default, which is none, the program runs and completes normally, throwing no exceptions and causing no errors.

My question is, can I safely ignore this (because MSVC++ could be somehow wrong) or is this a real problem? I don’t see how the program can continue successfully when the stack has been screwed up.

---

Edit:

The function that causes this error looks exactly like this:

int fun(list<int>::iterator&, const list<int>::iterator&);

int foo(list<int>& l) {
    list<int>::iterator beg = l.begin();
    list<int>::iterator end = l.end();
    return fun(beg, end);
}

fun increments and operates on beg and when it returns, beg == end, and when MSVC++ breaks, it points to the closing }.

---

Edit 2:

I have isolated the problem. In some situations, fun removes some elements from the list who owns the items it iterates. This is what causes the error.

Answer 1

Your question isn’t answerable without code to reproduce the problem.

But to give a vague answer to your general problem – If the compiler or debugger detected a problem, you probably have one.

In C++, just because something “goes wrong” doesn’t mean your program will crash – it might keep running with completely unpredictable results. It may even complete with the results you desired. But just because it ran well on your system doesn’t give you any guarantee for other systems, compilers, times of day, or even for additional runs of the same program.

This is called undefined behavior, and is caused by using the language incorrectly (but not in a way that causes a compile failure). A buffer overrun is only one of dozens of examples.