How do I erase elements of vector<> with an index?

std::vector<int> vec;

vec.push_back(6);
vec.push_back(-17);
vec.push_back(12);

// Clear the second element (vec[1])
vec.erase(vec.begin() + 1);

// Erase 2nd to 3rd elements (vec[1], vec[2])
vec.erase(vec.begin() + 1, vec.begin() + 3);