Is there a built in function for std::string in C++ to compare two strings alphabetically when either string can be uppercase or lowercase?

Question

I know for C++ that basic comparative operators can accomplish the task if both words are either entirely lower or entirely upper case. I have an array of strings and letter

Answer 1

I don't know of any case-insensitive functions in the standard library, but you can specify a custom predicate for std::equal:

std::string a("hello");
std::string b("HELLO");
std::cout << std::equal(a.begin(), a.end(), b.begin(),
    [] (const char& a, const char& b)
    {
        return (std::tolower(a) == std::tolower(b));
    });

For a solution which takes locale into account, refer to Case insensitive std::string.find().

#include 

template
struct my_equal {
    my_equal( const std::locale& loc ) : loc_(loc) {}
    bool operator()(charT ch1, charT ch2) {
        return std::toupper(ch1, loc_) == std::toupper(ch2, loc_);
    }
private:
    const std::locale& loc_;
};

int main()
{
    std::string a("hello");
    std::string b("HELLO");
    std::cout << std::equal(a.begin(), a.end(), b.begin(),
        my_equal<>(std::locale()));
}