what is the difference between overloading an operator inside or outside a class?

In C++, i know there are two ways to overload. We can overload it inside (like class a ) or outside (like class b ). But, the question is, is there any difference between these two either in compile time or runtime or not?

class a
{
public:
    int x;
    a operator+(a p) // operator is overloaded inside class
    {
        a temp;
        temp.x = x;
        temp.x = p.x;
        return temp;
    }
};

class b
{
public:
    friend b operator+(b, b);
    int x;
};

b operator+(b p1, b p2) // operator is overloaded outside class
{
    p1.x += p2.x;
    return p1;
}

---

成员operator+要求LHS成为a - 免费运营商要求LHS或RHS是b而另一方可以转换为b

struct Foo {
    Foo() {}
    Foo(int) {}
    Foo operator+(Foo const & R) { return Foo(); }
};


struct Bar {
    Bar() {}
    Bar(int) {}
};

Bar operator+(Bar const & L, Bar const & R) {
    return Bar();
}


int main() {
    Foo f;
    f+1;  // Will work - the int converts to Foo
    1+f;  // Won't work - no matching operator
    Bar b;
    b+1;  // Will work - the int converts to Bar
    1+b;  // Will work, the int converts to a Bar for use in operator+

}

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