C++11 vector constructor copy vs range?

Question

I can't understand the advantages of or differences between vector copy constructors and range constructors. When I construct three vectors like this:

    vector<int> FirstVec(3, 911); //fill constructor
    vector<int> SecondVec(FirstVec.begin(), FirstVec.end()); //range constructor
    vector<int> ThirdVec(FirstVec); //copy constructor

The contents of SecondVec and ThirdVec are exactly the same. Are there any scenarios in which using one of them has advantages? Thank you.

Answer 1

The range constructor is quite useful when you want to copy the items of a different type of container, or don't want to copy a full range. For example

int a[] = {1,2,3,4,5};
std::set<int> s{3, 911};
std::vector<int> v0{1,2,3,4,5};

std::vector<int> v1(std::begin(a), std::end(a));
std::vector<int> v2(a+1, a+3);
std::vector<int> v3(s.begin(), s.end());
vector<int> v4(v0.begin(), v0.begin() + 3);