C ++：从模板参数继承

Question

In the next code example:

#include <iostream>
using namespace std;
int f() {
    return 0;
}
struct A {
    int f()    {
        return 1; }
};
template<class T>
struct C : public T {
    C() {
        cout << f() << endl;
    } };
int main() {
    C<A> c; // prints 0
    return 0;
}

If I change the inheritance to be non-template like this: struct C : public A

then it prints "1" and not 0.

Why is that?

Answer 1

in f() , f is a nondependent name, so name lookup happens at template definition time (before T is known) and binds it to ::f . If you want it to call the member function f, then use this to make it a dependent name:

template<class T>
struct C : public T {
    C() {
        cout << this->f() << endl;
    } 
};