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;
}

---

I'd say that in this case, it really is a matter of style, and both are fine. The former has the advantage of being more consistent since strings are normally passed by (const) reference; the latter has the advantage of being a little less verbose.

Note that the const for the latter is wrong. You actually want to change s, so s should be non-const.

I see. Thanks for the correction. Is there any performance difference?

Quote:

---

Is there any performance difference?

---

The MinGW port of g++ 3.4.5 does produce different assembly code for the two cases, but I am afraid that I have neither the time nor skill at the moment to determine if this makes for any real difference in efficiency.

That said, I daresay that there is no real difference: the time will likely be dominated by the copying of characters, which is the same in both cases. If you are particularly concerned, profile your code.

If the string you pass is not already a variable, the latter is faster.

Code:

---

string s = transform1("Hello, World!");

---