How do I find the number of objects that are alive in C++?

I want to find the objects of a class that are currently alive in C++. Please tell me a solution for this. Also, please correct if my logic is wrong!

• Declare a global variable.
• Increment it during the constructor invocation.
• Decrement during dest开发者_如何学Cructor invocation.

Thanks in advance.

Sanjeev

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keep a static variable in your class as count. Global variables are not good practice.

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Your logic is correct except for one thing: don't make it a global variable; it is untidy and there is the danger that a bug in some other code might modify it. Instead make it a private static member variable of the class.

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Take a look at the curiously recurring template pattern, it is great for this sort of thing and the example in wikipedia shows how to use it for an object counter.

template <typename T>
struct counter
{
    counter()
    {
        ++objects_created;
        ++objects_alive;
    }

    virtual ~counter()
    {
        --objects_alive;
    }
    // if you are using multiple threads, these need to be protected
    // with interlocked operations as appropriate per your compiler + platform
    static int objects_created;
    static int objects_alive;
};
template <typename T> int counter<T>::objects_created( 0 );
template <typename T> int counter<T>::objects_alive( 0 );

class X : counter<X>
{
    // ...
};

class Y : counter<Y>
{
    // ...
};

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It's impossible in C++. Tracking constructor and destructor does not guarantee the accuracy: how do you prevent a memory copy like this:

memcpy(buf, &instance, sizeof(T));
T* anotherInstance = (T*)buf;