c++ - How do you get a "pointer to self" from within a class?

Question

In a method of an object of type class A, I handle an object of class B that has a public method .join(*A).

I want my object of type A calling this someObjectOfTypeB.join(*A) method, to use a pointer to itself as the parameter.

void A::someMethod()
{
    B b();
    b.join(I want to a to use a pointer to itself as a parameter);
}

A a();
a.someMethod();

Upon further investigation, this was not the problem as I led myself to believe; and is indeed the correct way of doing what I wanted to do.

You are declaring `b` as a _function_ here, taking void and returning a `B`. Is this what you want? — Andrew Lazarus, Nov 23 '14 at 01:58
`*A` is not a valid type. Did you mean `A*` for `join`'s parameter type, or did you mean that given a suitable expression `A`, `join` can be called as `join(*A)`? — , Nov 23 '14 at 02:05
@JonathanWakely: If you actually read that article you'll see that this is _not_ the most vexing parse, and I wish people would stop spreading the myth that it is. It is merely related to the MVP. — Lightness Races in Orbit, Nov 23 '14 at 02:11
@Werner, I suspect you have got confused by the error message due to declaring `B b()`, which does not do what you think it does (as the comment above says, it declares a function). Try `B b; b.join(this);` (N.B. that's `B b;` _not_ `B b();`) — Jonathan Wakely, Nov 23 '14 at 02:15
@LightnessRacesinOrbit, I didn't say it _is_ the MVP, I just pointed to the wikipedia page which covers similar cases, but I've replaced the comment anyway. Do you have a better reference (such as an SO answer) for "that's not a default-initialization it's a function declaration"? — Jonathan Wakely, Nov 23 '14 at 02:16
@JonathanWakely: Unfortunately, silly people keep closing them as dupes of confused MVP questions, but http://stackoverflow.com/questions/180172/default-constructor-with-empty-brackets isn't too bad if you ignore the constant propagation of the same myth throughout its answers. — Lightness Races in Orbit, Nov 23 '14 at 02:31

AlexD · Accepted Answer · 2014-11-23T02:14:43.847

6

Try using this:

void A::someMethod()
{
    B b;
    b.join(this);
}

As @AndrewLazarus and @JonathanWakely commented, use B b; instead of B b(). The later declares a function b without parameters which returns B, and that is not what you want.

edited Nov 23 '14 at 02:14

answered Nov 23 '14 at 01:54

AlexD

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This is actually saying: b.join(pointer to b); This is why I am posting, because I tried that :( – Werner Nov 23 '14 at 01:55
1

@Werner Do you mean `b.join(&b)`? – AlexD Nov 23 '14 at 01:58
Perhaps... regardless, I want the paramter to be of a's own self, not b – Werner Nov 23 '14 at 01:59
2

@Werner `A`'s own self, within `A`, it `this`. Or did I misunderstand? – AlexD Nov 23 '14 at 02:01
1

@Werner: You misunderstand how it works. Inside `A::someMethod()`, `this` refers to the instance of class `A`. – Jonathan Potter Nov 23 '14 at 02:05
Don't reference comments in answers - comments are transient and will be deleted at any time. Instead, adapt the words you're referring to into your own post. – Lightness Races in Orbit Nov 23 '14 at 02:10
@LightnessRacesinOrbit As you wish :). – AlexD Nov 23 '14 at 02:12

c++ - How do you get a "pointer to self" from within a class?

1 Answers1