operator==

template<class BidIt>
    bool operator==(
        const sub_match<BidIt>& left,
        const sub_match<BidIt>& right);
template<class BidIt, class IOtraits, class Alloc>
    bool operator==(
        const basic_string<typename iterator_traits<BidIt>::value_type, 
        IOtraits, Alloc>& left,
        const sub_match<BidIt>& right);
template<class BidIt, class IOtraits, class Alloc>
    bool operator==(
        const sub_match<BidIt>& left,
        const basic_string<typename iterator_traits<BidIt>::value_type, 
        IOtraits, Alloc>& right);
template<class BidIt>
    bool operator==(
        const typename iterator_traits<BidIt>::value_type* left,
        const sub_match<BidIt>& right);
template<class BidIt>
    bool operator==(
        const sub_match<BidIt>& left,
        const typename iterator_traits<BidIt>::value_type* right);
template<class BidIt>
    bool operator==(
        const typename iterator_traits<BidIt>::value_type& left,
        const sub_match<BidIt>& right);
template<class BidIt>
    bool operator==(
        const sub_match<BidIt>& left,
        const typename iterator_traits<BidIt>::value_type& right);
template<class BidIt, class Alloc>
    bool operator==(
        const match_results<BidIt, Alloc>& left,
        const match_results<BidIt, Alloc>& right);

Each template operator converts each of its arguments to a string type and returns the result of comparing the converted objects for equality.

When a template operator converts its arguments to a string type it uses the first of the following transformations that applies:

arguments whose types are a specialization of template class sub_match are converted by calling the str member function;
arguments whose types are a specialization of the template class basic_string are unchanged;
all other argument types are converted by passing the argument value to the constructor for an appropriate specialization of the template class basic_string.