Question

The interviewer showed me a code like this and asked me whether it would compile, and give my reasoning. I told him very certainly that it will not compile, because 10 is a constant and you cannot assign a constant to a non-const reference (like int& b = 10 will not compile), also, _a is a temporary variable and it is also considered const, again, you cannot use non-const reference to refer a const variable.

However, after I came home to my surprise I found it compile perfectly with all possible compilers. Also, I didn’t get the job. What part of my understanding went wrong?

class A {
    int& a;
public:
    A(int _a):a(_a) {}
};

int main() {
    A a(10);
}    

Answer 1

there is no “assignment” of a const with this code…

The code calls the constructor which takes an int and in turn calls the initializer of the int& . You skipped several steps the compiler sees/takes when you assumed it meant int& b = 10 while it is more like _a = 10; int& a = _a;. it compiles but is cerainly nothing you would want to use (binding a reference to stack which later on will lead to undefined behaviour/corruption)…