Why does the standard let functions that don't return compile?

Question

f() does not return even though it's signature say it should. Why is the reason for allowing this to compiling? Is there a reason the C standard does not require the compiler to make it fail?

I know that it is Undefined behavior and all, but why is it allowed in the first place? Is there a historical reason?

double f(){}

int main()
{
    f();
    return 0;
}

Answer 1

Is there a reason the C standard does not require the compiler to make it fail?

By invoking undefined behavior, the C standard allowed the compilers to be less complicated. There is indeed some cases, such as if statements, in which it is hard to say whether the function returns a value or not:

int f(int n)
{
  if (n > 0) return 1;
}

• If I write f(5), it is easy for the compiler to say that the function is correct.
• If I write f(-5), it is also easy to detect an undefined return value.

But if the argument comes from user input for example, how should the compiler be able to know whether the function returns a value? Since this could both a valid or a wrong program, C standard allows the compilers to do what they want. C is designed to be as smart and simple as possible.