std::regex_token_iterator<BidirIt,CharT,Traits>::operator++, operator++(int)

From cppreference.com
regex_token_iterator& operator++();
(since C++11)
regex_token_iterator operator++(int);
(since C++11)

Advances the iterator on the next sub match.

If *this is a suffix iterator, sets *this to an end-of-sequence iterator.

Otherwise, if N + 1 < subs.size(), increments N and sets result to the address of the current match.

Otherwise, sets N to 0 and increments position. If position is not an end-of-sequence iterator the operator sets result to the address of the current match.

Otherwise, if any of the values stored in subs is equal to -1 and prev->suffix().length() is not 0 the operator sets *this to a suffix iterator that points to the range [prev->suffix().first, prev->suffix().second).

Otherwise, sets *this to an end-of-sequence iterator.

The behavior is undefined if the iterator is end-of-sequence iterator.

Parameters

(none)

Return value

1) *this
2) The previous value of the iterator.