I am overloading the operator equals (==) as show bellow:

#include <string>
#include <algorithm>

bool operator == (std::string str1, std::string str2) {
    std::transform(str1.begin(), str1.end(), str1.begin(), ::tolower);
    std::transform(str2.begin(), str2.end(), str2.begin(), ::tolower);
    return (str1 == str2);
}

but, the problem appear on line return (str1 == str2), because operator == is called recursively. So, how can I call the original definition for operator equals (not the overloaded) ?

Best regards