如何一个类树的一个分支的所有零初始化成员是垃圾？ [英] How can one branch of class tree have all its Zero initialized members be rubbish?

问题描述

（只有当零初始化为静态作用域成员时才是垃圾），并且其工作原理如同GCC中预期的那样（） （（

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

所以代码如下：

#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;
}

其中所有类通常是POD（ ints ， enums ）我得到下一个输出：

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

而我期望所有的 0 ！

为什么会发生这种情况？

Why can such thing happen?

推荐答案

编译器错误：根据此报告基类的成员在派生类的值初始化期间不是零初始化。

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.

就我所见，你的代码没有什么问题，所有的类成员都应该在一个合格的C ++ 03或C ++ 11编译器上进行初始化。

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.

我想你的选择是：

• 通过避免继承使类更像POD类似;或


• 将默认构造函数添加到任何基类，以显式零初始化所有成员;或


• 使用较少损坏的编译器。

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