Primitive to user defined assignment on construction

Sorry for the blurry title, I seem to be missing something.

I was hesitant to post this, because it seems so basic, but I can't get it to work. My IDE tells me the fo开发者_运维技巧llowing is incorrect. I have a class called IRatio which I want to be interchangeable with long double.

class
IRatio
{
    protected:
        long double 
        mValue;

    public:
        IRatio();

        IRatio(
            const IRatio& ir);

        IRatio(
            const long double& ld);

        IRatio&
        operator=(
            const IRatio& ir);

        IRatio&
        operator=(
            const long double& ld);

        operator long double() const;
};

Now I know that the following lines work:

IRatio n1(0.01f);
IRatio n2;
n2 = 0.02f;

However, to my complete suprise, this line doesn't work:

IRatio n3 = 0.03f;

How do I get this to work? I assumed the copy constructor was called in this case? Or even if it was the assignment operator, I don't mind! I know that std::string can do it.

std::string s = "hello!";

Thanks

Your code should work as is. That said, IRatio doesn't manage any resources on its own, so you don't need the copy constructor and assignment operator. This should do:

struct IRatio {
    IRatio() : d(0L) { }
    IRatio(long double d) : d(d) { }
    operator long double() const { return d; }
private:
    long double d;
};

int main(int argc, char* argv[])
{
    IRatio r = 0.02f;
    return 0;
}

Your code should work. However, 0.03f is of type float. You want to say 0.03L to say long double. But this doesn't necessarily matter here, float is convertible to long double.

Yes, the constructor with parameter const long double& would be used to create a temporary IRatio object, which would be copied to n3 (and your compiler should optimizes the copy, so you are likely not to see a copy constructor call here, unless you have told it not to optimize).