I'm unable to define a function able to receive NULL or "" if I want

[tonnot]

I want to pass a "" or NULL value to a function which has the operator << overloaded.
I have :

myclass::operator << (std::string data) {}
 
myclass::operator << (const char * data) {}
 
myclass::operator << (bool data) {}

myclass::operator << (std::string data) {}

myclass::operator << (const char * data) {}

myclass::operator << (bool data) {}

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Ok , if I call class<<""; I see that function used is the bool ???????

How can I do to detect "" or NULL ???? What kind of types are ?
Any help ? Thanks