Random output with char* operator

Question

I have a class in c++, and I would like to be able to print an object, so I created a char* cast operator. The thing is that for some reason the output of the operator function is random symbols instead of my returned string. here's the code:

operator const char*()const {
    std::cout << (std::to_string(Nom) + '/' + std::to_string(Denom)).c_str() << std::endl;
    return  (std::to_string(Nom) + '/' + std::to_string(Denom)).c_str();
}

and the main function:

Rational r1(7, 15);
std::cout << r1<<std::endl;
return 0;

The first line output normaly ("7/15"), but the return value is just random letters.

Any clues?

Answer 1

A complement to others answers: usually an implicit cast operator is a bad style. Especially a cast to a type that is not related with your class's one.

If you want to cast your object, the better way may be an explicit cast:

class Rational
{
public:
    ...
    std::string toString() const
    {
        return std::to_string(Nom) + '/' + std::to_string(Denom);
    }
};

You can overload an "out" function with it:

std::ostream & operator <<(std::ostream &stream, const Rational &obj)
{
    stream << obj.toString();
    return stream;
}

If you need only to out your object, you also can use an overload without cast function:

class Rational
{
public:
    ...
    friend std::ostream & operator <<(std::ostream &stream, const Rational &obj)
    {
        stream << std::to_string(obj.Nom) + '/' + std::to_string(obj.Denom);
        return stream;
    }
};