Question

I’d like to place the last three values of vector v_2 in three variables (one value per variable).
Is there a faster or simpler way to do this?

struct Desempenho {
double maximo;
};  

 double ultimo, penultimo, antepenultimo;
 Desempenho d;
 int n (0);
 vector<Desempenho> v_2;
 d.maximo=1.1;
 v_2.push_back(d);
 d.maximo=2.2;
 v_2.push_back(d);
 d.maximo=3.3;
 v_2.push_back(d);
 d.maximo=4.4;
 v_2.push_back(d);
 d.maximo=5.5;
 v_2.push_back(d);

 for (vector<Desempenho>::const_reverse_iterator rit = v_2.rbegin(); rit != v_2.rend(); ++rit) {
     cout << "XXXX " << n << endl;
     if (n==0) ultimo = rit->maximo;
     else if (n==1) penultimo = rit->maximo;
     else if (n==2) antepenultimo = rit->maximo;
     else break;
     ++n;
     }

 cout << ultimo << " " << penultimo << " " << antepenultimo <    < endl;

Answer 1

Well, you don’t need a loop to use iterators:

vector<Desempenho>::const_reverse_iterator rit = v_2.rbegin();
if (rit != v_2.rend()) {
    ultimo = rit->maximo;
    if (++rit != v_2.rend()) {
        penultimo = rit->maximo;
        if (++rit != v_2.rend()) antepenultimo = rit->maximo;
    }
}

If you want to be needlessly flashy:

size_t len = v_2.size();
switch(len) {
    default:
        antepenultimo = v_2[len-3].maximo;
    case 2:
        penultimo = v_2[len-2].maximo;
    case 1:
        ultimo = v_2[len-1].maximo;
    case 0:
        break;
}

But your code reviewer will throw a biro at your head. More sensibly, a single error-check might do:

size_t len = v_2.size();
if (len >= 3) {
    ultimo = v_2[len-1].maximo;
    penultimo = v_2[len-2].maximo;
    antepenultimo = v_2[len-3].maximo;
}