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"Pang Fu" <nospam_pangfu@hotmail.com> wrote in message
news:3f0a59ff@newsgroups.borland.com...
> How to count how many instances are created
> of a user defined class?

Add a static member to the class, then increment it in the constructor and
decrement it in the destructor.

> In the following example how TMyClass can count
> the number of instances (objects created from TMyClass) ?

>    InstanceCount ++; <--?? How to start from zero and increment?

Static members must be defined separately from the class declaration.
Simply declare the variable to have an initial value of 0 when you define it
in your source file:

    --- header file ---

    class TMyClass
    {
    public :
        // InstanceCount must be public if you intend to access it directly
otherwise
        // you will need to declare a public method to return the value
instead
        static int InstanceCount;
        TMyClass() { ++InstanceCount; }
        ~TMyClass() { --InstanceCount; }
    };


    --- source file ---

    int TMyClass::InstanceCount = 0;


>    const int N= 456;
> for (int i=0; i<N; i++){
>   TMyClass *MyObj = new TMyClass();
> }

You do realize that you have a memory leak there, don't you?  You are
allocating 456 instances of the class dynamically, but are never freeing
them.

> AnsiString S;
> S.sprintf("Instance Count :%d", ????How????);

    S.sprintf("Instance Count :%d", TMyClass::InstanceCount);


Gambit