Efficient C++ Performance Programming Techniques

Eliminate Temporaries with op=()

In the previous discussion we have supplied the compiler with an existing object to work with so it will not invent a temporary one. That same idea can get recycled in other situations as well. Suppose that s3 does have a previous value and we are not in position to initialize s3 from scratch with:

string s3 = s1 + s2;

If we are looking at the case:

{
    string s1,s2,s3;
    ...
    s3 = s1 + s2;
    ...
}

we can still prevent the creation of a temporary. We can do that by using the string operator+=() and rewriting the code to use += instead of +, so

s3 = s1 + s2;      // Temporary generated here

is rewritten as:

s3  = s1;      // operator=(). No temporary.
s3 += s2;      // operator+=(). No temporary.

If string::operator+=() and ...