std::back_insert_iterator::operator++

From cppreference.com
back_insert_iterator& operator++();
back_insert_iterator& operator++( int );

Does nothing. These operator overloads are provided to satisfy the requirements of OutputIterator. They make it possible for the expressions *iter++=value and *++iter=value to be used to output (insert) a value into the underlying container.

Parameters

(none)

Return value

*this