How to create a method that compares an unknown number of strings in C++?

Question

After some research I found that in C++ I can create a function with infinite variables in this way:

template<typename ... Args>
void func(Args... a) {
    /* CODE */
}

I want to make a method that compares an unknown number of strings and gives a bool: true if are equal and false if are not equal.

I did something like this but I don't know how to iterate the strings.

template<typename ... Strings>
bool cmp(string first, Strings... rest) {
    /* ITERATE AND COMPARE */

    return false;
}

So how I can iterate them?

Answer 1

The term infinite variables is not correct. C++ can handle variable numbers of function arguments but not infinitely many ones.

If you can use C++17 a fold expression would be the easiest solution:

template<typename ... Ts>
bool cmp(const std::string& first, const std::string& second, const Ts&... rest) {
    return (cmp(second, rest) && ... && (second == first));
}

Again using C++17 you can also use a recursive approach using if constepxr:

template<typename ... Ts>
bool cmp(const std::string& first, const std::string& second, const Ts&... rest) {
    if constexpr (!sizeof...(Ts)) {  // Do we have only two arguments left?
        return first == second;
    } else {
        return first == second && cmp(second, rest...);
    }
}

For C++14 you can simply overload the two argument version and use again recursion:

bool cmp(const std::string& first, const std::string& second) {
    return first == second;
}

template<typename ... Ts>
bool cmp(const std::string& first, const std::string& second, const Ts&... rest) {
    return first == second && cmp(second, rest...);
}