std::string a = "apple", b = "AbPlE"; // Just returns true or false bool result = std::equal(a.begin(), a.end(), b.begin(), b.end(), [] (char x, char y) { return std::tolower(x) == std::tolower(y); }); // Returns a pair with the iterators where the string first mismatched auto position = std::mismatch(a.begin(),   a.end(),   b.begin(),   b.end(),   [] (char x, char y)   { return std::tolower(x) == std::tolower(y); });

println(result, ", ", std::distance(a.begin(), position.first));

Implementations:

template<typename I, typename J, typename Predicate> bool eq(I i, I j, J k, J l, Predicate predicate) { for ( ;i != j && k != l; ++i, ++k) { if (! predicate(*i, *k)) return false; } return i == j && k == l; } template<typename I, typename J, typename Predicate> std::pair<I, J> mism(I i, I j, J k, J l, Predicate predicate) { for ( ;i != j && k != l; ++i, ++k) { if (! predicate(*i, *k)) break; } return {i, k};

}