std::char_traits<char>::length, std::char_traits<wchar_t>::length, std::char_traits<char8_t>::length, std::char_traits<char16_t>::length, std::char_traits<char32_t>::length

#include <iomanip>
#include <iostream>
#include <string>

void print(const char* str)
{
    std::cout << std::quoted(str) << "   = "
              << std::char_traits<char>::length(str) << '\n';
}

int main()
{
    print("foo");
    
    std::string s{"booo"};
    print(s.c_str());
}