The trouble with boost is that you have to link with and depend on boost. Not easy in some cases (e.g. android).

And using char_traits means all your comparisons are case insensitive, which isn't usually what you want.

This should suffice. It should be reasonably efficient. Doesn't handle unicode or anything though.

#include <cctype>    // std::tolower
#include <algorithm> // std::equal

bool ichar_equals(char a, char b)
{
    return std::tolower(static_cast<unsigned char>(a)) ==
           std::tolower(static_cast<unsigned char>(b));
}

bool iequals(const std::string& a, const std::string& b)
{
    return a.size() == b.size() &&
           std::equal(a.begin(), a.end(), b.begin(), ichar_equals);
}

C++14 version

#include <cctype>    // std::tolower
#include <algorithm> // std::equal

bool iequals(const std::string& a, const std::string& b)
{
    return std::equal(a.begin(), a.end(), b.begin(), b.end(), ichar_equals);
}

C++20 version using std::ranges

#include <cctype>      // std::tolower
#include <algorithm>   // std::equal
#include <string_view> // std::string_view

bool iequals(std::string_view lhs, std::string_view rhs)
{
    return std::ranges::equal(lhs, rhs, ichar_equals);
}