使用STL迭代器而不初始化它

vector<int> v = {1, 2, 3, 4, 5};
vector<int>::iterator it = v.begin();

for (vector<int>::iterator it = v.begin(); it != v.end(); ++it) {
    cout << *it << " ";
}

vector<int> v = {1, 2, 3, 4, 5};
vector<int>::iterator it1 = v.begin();
vector<int>::iterator it2 = v.end();
if (it1 == it2) {
    cout << "Equal iterators"<< endl;
}

vector<int> v = {1, 2, 3, 4, 5};
vector<int>::iterator it = v.begin();
cout << *it<< endl;