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#include<iostream>
int& f(){
static int x = 0;
x++;
return x;
}
int main(){
f() += 1; //A
f() = f() + 1; //B
std::cout << f();
}
The above code outputs 6 on gcc and 5 on MSVC. Now when I modify A and B to f()=f() I get 5 on both compilers. What is the big deal here? Is the behavior undefined. If yes , why?
It is undefined, because in this code:
it is not defined which call to f() happens first.