Retrieves a const iterator to the first element in a specified container.
This function works with all STL containers and with initializer_list.
You can use this member function in place of the begin() template function to guarantee that the return value is const_iterator. Typically, it's used in conjunction with the auto type deduction keyword, as shown in the following example. In the example, consider Container to be a modifiable (non-const) container or initializer_list of any kind that supports begin() and cbegin().