Using "<<" or "+" to put strings together when using "cout"

Question

I have seen people output different strings together by using both "<<" and "+".

cout << firstname << lastname << endl;

versus:

cout << firstname + lastname << endl;

Is it better to use "<<" or does it not make much of a difference?

Answer 1

I would say its better to use << in that particular case. Otherwise, concatenation results in a temporary which could allocate memory for no good reason.

Answer 2

Definitely, use << - concatenating the string will create a copy of the two strings pasted together. Whether it also allocates extra memory on top is a matter of how strings are implemented in the C++ library, but if the first and last names are "long enough" (bigger than 8-16 characters together), then it most likely WILL allocate memory (and then free it again when the temporary copy is no longer needed).

The << operator will have very little overhead in comparison, so no doubt it is better.

Of course, unless you do thousands of these things, it's unlikely that you will have a measurable difference. But it's good to not waste CPU cycles, you never know what good use they can be somewhere else... ;)