<< operator vs. overloaded + operator for strings in C++

Question

Is there is difference between the two following lines of code?

(Perhaps in efficiency or something of that nature?)

const std::string a = "a";
const std::string b = "b";

std::cout << a << " comes before " << b << "\n";
std::cout << a + " comes before " + b + "\n";

Answer 1

Yes:

The first line calls operator<< of std::cout (of type std::ostream). It prints each of its operands.

The second line calls operator+ of std::string, which creates multiple temporary std::string objects which then eventually call operator<< which prints them.

Prefer the first because it avoids temporary objects, and works better. Consider the situation were a and b have type int. The first version continues to work the second will no longer work.