Thread: What is a better style?

I have some functions which perform string transformations. Since they use the original string, but return a copy of the modified string, what is better style?

Code:

string transform1(const string& s) { //uses const reference
	string s2 = s; //make a copy
	//do some stuff on the copy
	return s2;
}

string transform2(string s) { //passed by value
	//do some stuff on the copy already passed in
	return s;
}