member initial list, C++ (gcc)

member initial list

//g++  5.4.0

#include <iostream>
using std::cout;

class Obj{
public:
    Obj(){
        cout<<"call default ctor\n";
    }
    
    Obj(const Obj& c){
        cout<<"call copy ctor\n";
    }
    
    Obj(int val){
        cout<<"call other ctor\n";
    }
    
    ~Obj(){
        cout<<"destroy obj\n";
    }
};

class Test : public Obj // inherit from Obj
{
    // 3 member
    Obj a;
    Obj b;
    Obj c;
public:
    Test() // this ctor construct base class by Obj(), and members from a to c by Obj()
    {
        cout<<"Test call default ctor\n";
    }
    
    Test(int val)
        :Obj(val), // construct base class by Obj()
        a(),       // construct by Obj()
        b(val),    // construct by Obj(int val)
        c(this->b) // construct by Obj(const Obj& c)
        {
            cout<<"Test call other ctor\n";
        }
    
};

int main()
{
    Test a;      // would call default ctor.
    cout<<"-----------------------\n";
    Test b();    // would call defalt ctor, but not construct any object.
    cout<<"-----------------------\n";
    Test c(10);  // would call Test(int).
    cout<<"-----------------------\n";
    Test* d = new Test();    // call Test().
    cout<<"-----------------------\n";
    Test* e = new Test(10);  // call Test(int).
    cout<<"-----------------------\n";
}


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