inheritance_ctor_calls.cpp


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/* g++ -Wall -std=gnu++98 -pedantic -MD -O0 -g inheritance_ctor_calls.cpp -o inheritance_ctor_calls
 *
 * Note: line 64 is very IMPORTANT!
 * output:
 *
 * node1 default ctor called
 * node2 default ctor called with y
 * node1 default ctor called
 * node2 copy ctor called
 *
 */

#include <iostream>

class Node1
{
  public:
    Node1() : x_(0) {
        std::cout << "node1 default ctor called\n";
    };
    Node1(int x) : x_(x) {
        std::cout << "node1 default ctor called with x\n";
    };

    virtual void foo() {
        std::cout << "node1 foo called\n";
    }

    int x_;
};

class Node2 : public Node1
{
  public:
    Node2() : y_(0) {
        std::cout << "node2 default ctor called\n";
    };
    Node2(int y) : y_(y) {
        std::cout << "node2 default ctor called with y\n";
    };

    Node2(const Node2 &n) : y_(0) {
        std::cout << "node2 copy ctor called\n";
    }

    virtual void foo() {
        std::cout << "node2 foo called\n";
        /* invoke parent method */
        Node1::foo();
        /* do things unique to this class */
        /* ... */
    }

    int y_;
};

class Collection : public Node2
{
  public:
    /* only immediate base class may be initialized, Node1 is 2 level deep here hence error */
    Collection() : /* Node1(2), error */ Node2(1), z(0) {
    }
    /* parent copy ctor needs to be invoked since derived class' copy ctor is overridden */
    Collection(const Collection& c) : Node2(c), z(0) {
        /* ... */
    }

    int z;
};

int main(int argc, char **argv)
{
    Collection c;
    Collection d(c);

    return 0;
}