Constructor with "this" in C++?

Question

In Java, we can write as following:

public class Demo{
    private int val;
    public Demo(int val){this.val = val;}
    public Demo(){this(0);}
}

However, it does not work in C++:

class Demo{
    private:
       int _val;
    public:
       Demo(int val):_val(val){}
       Demo(){this(0);}
}

How to revise this code?

billz · Answer 1 · 2014-01-11T11:08:20.680

8

With C++11, you could use delegate constructor:

Demo():Demo(0){ }

edited Jan 11 '14 at 11:08

answered Jan 11 '14 at 09:42

billz

44,644
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I'm pretty sure this just creates a temporary `Demo`. – user2357112 Jan 11 '14 at 09:43
1

I'll blame it on being tired, but `: Demo(0)` – chris Jan 11 '14 at 09:43
@chris Demo:Demo(0){} ? – allen.lao Jan 11 '14 at 09:48
2

@chris yes and I am a bit drunk as well after beer+ bbq – billz Jan 11 '14 at 09:50

Veritas · Answer 2 · 2014-01-11T09:59:32.553

4

class Demo{
    private:
       int _val;
    public:
       Demo(int val):_val(val){}
       Demo() :_val(0) {}
}

Or

class Demo{
    private:
       int _val;
    public:
       Demo(int val):_val(val){}
       Demo() :Demo(0) {}
}

edited Jan 11 '14 at 09:59

answered Jan 11 '14 at 09:43

Veritas

2,150
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Added the delegation way. I don't really see the point in this example though. – Veritas Jan 11 '14 at 09:51

score 1 · Answer 3 · answered Jan 11 '14 at 09:49

Or this approach which is useful when there are a lot of members to initialise (and before C++11):

class Demo{
    private:
       int _val;
       void Init( int val )
       {
           _val = val;
       }
    public:
       Demo(int val){Init(val);}
       Demo(){Init(0);}
}

Constructor with "this" in C++?

3 Answers3