Why there is no compiler error when return statement is not present?

Question

Unlike Java, in C/C++ following is allowed:

int* foo ()
{
  if(x)
    return p;
// what if control reaches here
}

This oft

Answer 1

What the standard says about this kind of programming is that it produces undefined behavior.

Undefined behavior is the joy and pity of C/C++, but it is also a fundamental feature of the language design that allows for many of the low-level optimizations that make C a sort of "high level assembler" (it is not, actually, but just to give you an idea).

So, while redirecting to John's answer about the switch to use with GCC, to know "why" the standard does not prevent that, I would point to a very interesting analysis of undefined behavior and all of its misteries: What Every C Programmer Should Know About Undefined Behavior. It makes for a very instructive reading.