Question

(not rubbish only if zero initialized as static scope member.) and it works as expected on GCC!(((

So for code like:

#include <iostream>
#include <boost/shared_ptr.hpp>

namespace SP
{
    // enums
    enum EnumMessage {
        EnumMessage_EventBase = 0,
        EnumMessage_EventServiceBase = 1,
        EnumMessage_OperationBase = 2
    };

    class Message;

    // define proxy class
    class Message  {
    public:
        EnumMessage _MessageCode;
    };

    class Parent : public Message {
    public:
        int _ServiceId;
        int _CallbackId;
    };

    class Child : public Parent {
    public:
        std::string _Debug;
    };

    class AnotherChild : public Parent {
    public:
        int _UserId;
    };
}

using namespace SP;

int main() {
    //OK
    static Child staticScopeChild = Child();
    boost::shared_ptr<Parent> ptrParent(new Parent());
    boost::shared_ptr<AnotherChild> ptrChild2(new AnotherChild());

    //Bad
    Child scopeChild = Child();
    boost::shared_ptr<Child> ptrChild(new Child());


    std::cout << "static " << staticScopeChild._MessageCode 
        << std::endl << "vs scope " << scopeChild._MessageCode 
        << std::endl << "vs pointer " << ptrChild->_MessageCode 
        << std::endl << "vs parent class pointer: " << ptrParent->_MessageCode 
        << std::endl << "vs another parent child: " << ptrChild2->_MessageCode <<std::endl;
    std::cin.get();
    return 0;
}

where all classes are generally PODs (ints, enums) I get next output:

static 0
vs scope -858993460
vs pointer -842150451
vs parent class pointer: 0
vs another parent child: 0

while I expected all to be 0!

Why can such thing happen?

Answer 1

It appears to be a compiler bug: according to this report members of base classes are not zero-initialised during value-initialisation of the derived class.

As far as I can see, there is nothing wrong with your code, and all class members should be zero-initialised on a conforming C++03 or C++11 compiler.

I guess your options are:

• make the classes more POD-like by avoiding inheritance; or
• add default constructors to any base classes to explicitly zero-initialise all members; or
• use a less broken compiler.