Does return statement copy values

Question

I am wondering about this because of scope issues. For example, consider the code

typedef struct {
    int x1;/*top*/
    int x2;/*bottom*/
    int id;
} sub         


        

Answer 1

I do not agree and NOT RECOMMEND to return vector to change values: Is much faster pass as reference:

void vectorial(vector  a, vector  b, vector  &c)
{
    c[0] = a[1] * b[2] - b[1] * a[2]; c[1] = -a[0] * b[2] + b[0] * a[2]; c[2] = a[0] * b[1] - b[0] * a[1];
}
//This is slow!!!:
vector  vectorial(vector  a, vector  b)
{
    vector  c{ a[1] * b[2] - b[1] * a[2], -a[0] * b[2] + b[0] * a[2], a[0] * b[1] - b[0] * a[1] };
    return c;
}

I tested on VS2015 with following results in release mode:

By reference:8.01 MOPs and returning vector: 5.09 MOPs 60% worse!

In debug mode things are much worse:

By reference:0.053 MOPS and return vector: 0.034 MOPs