Difference between vector::begin() and std::begin()

Question

While iterating over a vector in c++, I noticed there is a begin() function in the standard library, and also a begin() as a member function of the

Answer 1

The implementation of std::begin() for vectors simply calls std::vector<T>::begin(), so there is no difference between the two in this exact case.

Where std::begin() comes into its own is in generic algorithms:

template<typename Container>
void my_algorithm(Container c) {
    using std::begin;
    using std::end;
    auto const start = begin(c);  // ADL will find the appropriate overload
    auto const finish = end(c);
    // ... rest of code ...
}

Answer 2

std::begin() was added in C++11 to make it easier to write generic code (e.g. in templates). The most obvious reason for it is that plain C-style arrays do not have methods, hence no .begin(). So you can use std::begin() with C-style arrays, as well as STL-style containers having their own begin() and end().

If you're writing code which is not a template, you can ignore std::begin(); your fellow programmers would probably find it odd if you suddenly started using it everywhere just because it's new.