C++ :: Overloading Char And String Operators?

I build a nice class that i need the output be possible in char * and in string. But how I can do for the compiler don't be confused between them?

Code:
operator char*() {
return (char *) result.c_str();
}

These works fine. and for string, i must casting it. but i want do anotherone for string... how can i do it? I tried:

Code:
operator string() {
return result;
}

But the compiler stays confused or something