How does this function return a value when it shouldn't?

Question

This function returns a value even when it shouldn't.

#include<iostream>
using namespace std;
int foo(int a,int b)
{
    if(a>b)
        return a;
    else if(a<b)
        return b;
}
int main()
{
    int x=7,y=7;
    cout<<foo(x,y);
    return 0;
}

The output is:

Also it produces proper output only on a GCC compiler (I used Dev C++). Turbo C produced garbage value. Can someone explain how this happens?

It's undefined behavior, that simple. What would you expect as return value actually? — πάντα ῥεῖ, Nov 15 '16 at 17:15
I'm not expecting anything. I was wondering how it returns 7. — Subramanian Sridharan, Nov 15 '16 at 17:18
@SubramanianSridharan it can return anything. If you really want to know why it returns 7 with GCC you have to look at the generated assembly code. — Jabberwocky, Nov 15 '16 at 17:19

score 3 · Answer 1 · answered Nov 15 '16 at 17:15

3

The behaviour on not returning a value on all program control paths is undefined.

The compiler is allowed to do anything.

Didn't your compiler warn you of this? (GCC ought too, Turbo C possibly not on account of its age).

answered Nov 15 '16 at 17:15

Bathsheba

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Ironically, Turbo c gives a warning while Dev C++ doesn't! – Subramanian Sridharan Nov 15 '16 at 17:18
@SubramanianSridharan with proper settings Dev C++ will show a warning as well. – Jabberwocky Nov 15 '16 at 17:19
@SubramanianSridharan Switch on all warnings, and (assumed toolchain) GCC will warn you as well. – πάντα ῥεῖ Nov 15 '16 at 17:19

How does this function return a value when it shouldn't?

1 Answers1