Use SFINAE to call member function if present

main.cpp

#include <iostream>

class Foo {
public:
    void bar() {
        std::cout << "Foo::bar() called" << std::endl;
    }
};

class Foo2 {
};

// callBarIfPresent(T*)
// This version will be called if T::bar() exists:
template <class T> auto callBarIfPresent(T* obj) -> decltype(obj->bar()) {
    return obj->bar();
}
// This version will be called otherwise:
inline void callBarIfPresent(...) {
    std::cout << "No member function called" << std::endl;
}

int main()
{
    Foo foo;
    callBarIfPresent(&foo);

    Foo2 foo2;
    callBarIfPresent(&foo2);

    return 0;
}