cpp l-value vs r-value code| error: expected ',' or '...' before '&&' token, error: 'name' was not declared in this scope

Question

I am a newbie with this topic in cpp and trying to usnderstand through this code, so please tell me how l-values and r-values make difference in this code and how they are implemented. Also why am i getting error here (do execution of this code depends on c++ version)?

void printName(const std::string& name){
    std::cout << "[l-value] " << name << std::endl;
}
void printName(std::string&& name){ //Line 8
    std::cout << "[r-value] " << name << std::endl; //Line 9
}
int main(){
    std::string firstname = "Harry";
    std::string lastname = "Singh";

    std::string fullname = firstname + lastname;
    printName(firstname);
    printName(lastname);
    printName(firstname+lastname);
}

I am getting following mentioned error on the following code.

8 error: expected ',' or '...' before '&&' token
9 error: 'name' was not declared in this scope

Answer 1

rvalues references (&&) is a C++11 feature and onwards. It's because you're using C++98 or older:

Add this compiler flag -std=c++11 (or -std=c++14, -std=c++17, -std=c++20).