C++ ile kullanıcının girdiği ismi kontrol etme - Regex

/*Regex name checker, TerabyteForever*/
#include <iostream>
#include <regex>
#include <string>

int main(int argc, char** argv){
    std::string str = "";
    std::regex regex_;
    do{
        if(str != ""){
            std::cout<<"Invalid input."<<std::endl;
        }
        std::cout<<"Please enter your name: ";
        std::getline(std::cin,str);
        regex_ = std::regex("^$|(?:[^a-zA-Z ])"); //Anything that is not in a-z and A-Z range. Checks if the input is empty.
    } while(std::regex_search(str,regex_)); //If regex returns true, that means the input is invalid.
    return 0;
}