Accessing a class member in an if statement using std::is_same

Question

I\'m trying to tackle the following problem: I would like to do an if statement that does something depending on whether the argument of a template is a specific ob

Answer 1

In a regular if statement, both branches must be valid code. In your case int.length() makes no sense.

In C++17 you could simply use constexpr if:

if constexpr(std::is_same::value)
    std::cout << arg.length() << std::endl;
else
    std::cout << "The argument is not a string" << std::endl;

demo

In C++11 (or older) you can employ overloading to achieve similar result:

void foo(std::string const& str){
    std::cout << str.length() << std::endl;
}

template
void foo(T const&){
    std::cout << "The argument is not a string" << std::endl;
}

template 
void is_string(const T& arg) {
    foo(arg);
}

demo