计算单个派生类的实例 [英] Counting instances of individual derived classes

问题描述

我希望能够对属于同一类层次结构的类的实例进行计数.

I'd like to be able to count instances of classes that belong in the same class hierarchy.

例如，假设我有这个:

class A;
class B: public A;
class C: public B;

然后我有这段代码

A* tempA = new A;
B* tempB = new B;
C* tempC = new C;
C* tempC2 = new C;

printf(tempA->GetInstancesCount());
printf(tempB->GetInstancesCount());
printf(tempC->GetInstancesCount());

结果应打印
1
1
2

the result of that should print
1
1
2

理想情况下，应在内部进行计数.每个类(而不是某种管理器)都应该知道它有多少个实例.

The counting, ideally, should be done internally. Each class, and not some kind of manager, should know how many instances it has.

有什么想法吗?

谢谢！

推荐答案

建议的解决方案存在一个问题:创建B时，将自动调用A构造函数，从而增加A的计数.

There is a problem with proposed solutions: when you create B you A constructor will be called automatically and thus increment count of A.

class A
{
public:
    A(bool doCount = true)
    {
        if (doCount)
            ++instanceCount_;
    }

    static std::size_t GetInstanceCount()
    {
        return instanceCount_;
    }

    virtual ~A(){}
private:
    static std::size_t instanceCount_;
};

class B: public A
{
public:
    B(bool doCount = true):A(false)
    {
        if (doCount)
            ++instanceCount_;
    }

    static std::size_t GetInstanceCount()
    {
        return instanceCount_;
    }
private:
    static std::size_t instanceCount_;
};

std::size_t A::instanceCount_ = 0;
std::size_t B::instanceCount_ = 0;

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