这两种比较STL载体的方法有什么区别？

Question

Few examples available online use the equality operator to compare the contents of two STL vector objects in order to verify that they have the same content.

vector<T> v1;
// add some elements to v1

vector<T> v2;
// add some elements to v2

if (v1 == v2) cout << "v1 and v2 have the same content" << endl;
else cout << "v1 and v2 are different" << endl;

Instead, I read other examples where the std::equal() function is used.

bool compare_vector(const vector<T>& v1, const vector<T>& v2)
{
    return v1.size() == v2.size()
           && std::equal(v1.begin(), v1.end(), v2.begin());
}

What is the difference between these two ways to compare STL vectors?

Answer 1

The two behave in exactly the same way. The container requirements (Table 96) say that a == b has the operational semantics of:

distance(a.begin(), a.end()) == distance(b.begin(), b.end()) &&
equal(a.begin(), a.end(), b.begin())

Answer 2

Good question. I suspect that people don't use == because they don't know its there, but it does exactly what the hand-coded version does. It's always been there for sequence containers and for associative containers.