C++ Constructor Oder

Question

Consider the following piece of code:

#include<iostream>

using namespace std;

class cls

{

public:

        cls(int i=0) {cout<<" c1 ";}

        ~cls() {cout<<" d 1 ";}

};

class cls2

{

 cls xx;

public:

        cls1(int i=0){cout<<" c2 ";}

        ~cls1(){cout<<" d2 ";}

}c;

class cls3

{

    cls2 xx; cls xxx;

public:

    cls2(int i=0) {cout<<" c3 ";}

    ~cls2(){ cout<<" d3 ";}

};

int main()

{

    cls3 s;

    return 0;

}

Now, when I run it, it outputs:

c1 c2 c1 c2 c1 c3 d3 d1 d2 d1 d2 d1

and I can't seem to figure out why, in my head, it should output:

c1 c2 c1 c3 d3 d1 d2 d1

because:

cls2 s -> cls1 xx -> cls xx => c1

                           => c2

                -> cls xxx => c1

                => c3

I know that somewhere, my logic is flawed, but I don't know where.

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Answer 1

You are creating an extra global instance c here:

class cls1
{
    int x; cls xx;
public:
        cls1(int i=0){cout<<" c2 ";x=i;}
        ~cls1(){cout<<" d2 ";}
} c; // <-- here

That one is created first.

Otherwise your expected order is spot-on.

C++ Constructor Oder

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