c++ operator string and char* causing ambiguous error

Question

I'm trying to make a class with conversion operators to string and char*, this makes ambiguous call error when trying to create a string. assume i have the following class:

class A { public: A(){}; operator const char*() const { return "a" }; operator const string() const { return "b" }; }

and the following main programs:

int main() { A a; string b = string(a); return 0; }

this causing ambiguous call error to basic_string(A&) also tried the following:

class A { public: A(){}; operator const char*() const { return "a" }; explicit operator const string() const { return "b" }; } int main() { A a; string b = static_cast<string>(a); return 0; }

this causing the same error. I need to have both operators in my code, how can i make this work?

note: using string b = a works but I need the string(a) format to work aswell

note 2: not using explicit keywork makes operator= ambiguous

@πάνταῥεῖ Ah, yes, it should be compiled to the data segment. — Sergey
– Sergey, Commented Nov 16, 2016 at 10:04
@Sergey: It's not a local variable, it is a string literal. n4296 in 2.3.5 p16 says "Evaluating a string-literal results in a string literal object with static storage duration" (my emphasis). — Martin Bonner supports Monica
– Martin Bonner supports Monica, Commented Nov 16, 2016 at 10:06
Unrelated, but having the operator return const string is a pessimisation, because it prevents moving from the returned value. You should change it to just conver to string. — Angew is no longer proud of SO
– Angew is no longer proud of SO, Commented Nov 16, 2016 at 10:08

SingerOfTheFall · Accepted Answer · 2016-11-16 10:06:49Z

You need to make them both explicit and use static_cast:

class A { public: A(){}; explicit operator const char*() const { return "a"; }; explicit operator const string() const { return "b"; }; }; int main() { A a; string b = static_cast<string>(a); // works, b now has "b" as value const char * c = static_cast< const char *>(a); // works too, c now has "a" as value return 0; }

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