importance of vector::reserve

Not using reserve results in quite some extra work.

struct Foo
{
 static int i ;
 int f;
 Foo():f(i++){ cout << "in ctor:" << i << endl; }
 Foo(const Foo&):f(i++){ cout << "in copy ctor:" << i << endl; }
};
int Foo::i = 1;

void tst_vec()
{
 vector v;
 v.reserve(10);
 Foo f ;
 v.push_back(f);
 v.push_back(Foo());
 v.push_back(Foo());
 cout << "---" << endl;
 Foo& temp = v[0];
}

---

with reserve:
in ctor:2
in copy ctor:3
in ctor:4
in copy ctor:5
in ctor:6
in copy ctor:7
---

without reserve:
in ctor:2
in copy ctor:3
in ctor:4
in copy ctor:5
in copy ctor:6
in ctor:7
in copy ctor:8
in copy ctor:9
in copy ctor:10