C++ constructor: garbage while initialization of const reference

Question

what is wrong with this code, why do I get wrong answer:

class X
{
private:
        const int a;
        const int& b;
public:
        X(): a(10) , b(20)         


        

Answer 1

b refers to a temporary. What you have read (when printing) is an invalid location by the time it is read since the temporary 20 has technically gone out of scope.

To explain inconsistent results:

It is undefined behavior. What you see may be different if you:

• change your compiler
• change your compiler settings
• build for another architecture
• change your class' member layout
• add or remove things from the memory region near the instance of x
• etc.

You should always always avoid undefined behavior.

But why would the value change? Your reference likely refers to a stack address which has been rewritten (e.g. reused) by the time it's printed.