Where are the begin() and end() functions defined in C++?

Question

In cppreference.com, it states that the begin() and end() functions are defined in the header file < iterator > . But I still can use the begin() and end() functions without including the < iterator > header. I wonder why? Is it because I use;

using namespace std;

So it is included?

Answer 1

Read from notes on the same page :

In addition to being included in <iterator> , std::begin is guaranteed to become available if any of the following headers are included: <array> , <deque> , <forward_list> , <list> , <map> , <regex> , <set> , <string> , <unordered_map> , <unordered_set> , and <vector> .

Apart from these list of headers, std::begin may get included from some other header also.

Answer 2

No, using namespace xxx doesn't include any header files. It only means that you can write begin() instead of std::begin() . The <iterator> header must be included through some other header that you did include into your .cpp.