C ++运算符重载int类型

Question

I'm working on a fractions class in C++ and have defined the addition of a frac and an int in the new class, but it requires them to show up in that order: frac + int. Is there a way to overload + in the Int type such that we have a function that accepts a frac and outputs a frac? Or is there a way to reverse the order in the new class?

I already have frac + frac and frac += frac operators defined. The two functions in question are:

frac operator+=(int b)
{
    frac c = { n + b*d, d };
    return c;
}

frac operator+(int b)
{
    frac c = *this;
    frac d = { b };
    c += d;
    return c;
}

something like this:

frac int::operator+=(frac& b)
{
    frac c = { this * b.den() + b.num(), b.den() };
    return c;
}

But I'm not sure how to actually accomplish this.

---

Code from question below:

frac &operator+=(frac b)
{
    frac c = { n * b.den() + b.num() * d, d * b.den() };
    n = c.num();
    d = c.den();
    return *this;
}

frac operator+(int a, frac b)
{
    return frac{ a } += b;
}

Answer 1

Well there's no class int so you can't do what you suggested but the easy thing is to declare a function like this (inside your class)

 friend frac operator+(int a, frac b);

That way this function will be called when the other order is used. Edit: you need to use the friend specifier because the function isn't in the class, I forgot about that.

Answer 2

The proper way to do this is to make frac have an implicit constructor from int, and use a free operator+ so that conversions apply to both arguments. Also you can implement + in terms of += and so on. Eg

struct frac
{
    frac(int x) { /* initialize frac with x */ }

    frac &operator+=(frac f) { /* add f to this */ return *this; }
};

frac operator+(frac f1, frac f2)
{
    return f1 += f2;
}

Update : some people consider implicit conversion constructors to be bad style; if you're one of those then you can work around it by using an explicit constructor and writing a series of operators with exact parameters, eg

frac operator+(int f1, frac f2) { return frac(f1) += f2; }
frac operator+(frac f1, int f2) { return f1 += frac(f2); }
frac operator+(frac f1, frac f2) { return f1 += f2; }

Answer 3

Declare the member operators as static and you can have two parameters. See the declaration of WholeNumber -- the operators are static and have no instance of *this.

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