Two Object related question

This is a discussion on Two Object related question within the C++ Programming forums, part of the General Programming Boards category; How does one make an object null? I think in Java, one could merely do Code: anObject = null; but ...

  1. #1
    Some Guy
    Join Date
    Jul 2004
    Posts
    32

    Two Object related questions

    How does one make an object null? I think in Java, one could merely do
    Code:
    anObject = null;
    but I could be wrong. Basically, I have an array of objects and I want to delete one of the objects. I think null is the way to do it, no?

    Secondly, I have this..

    Code:
    class EmpArys
    {
    	public:
    		EmpArys();
    		int findEmp(int pSocSecNbr);
    		Employee getEmp(int pSocSecNbr);
    		bool addEmp(Employee pEmp);
    		bool delEmp(int pSocSecNbr);
    		string toString();
    		string getPayList(Tax pTaxTable);
    	private:
    		Employee empList[100];  //i've temporarily put 100 there
    		int empCount;
    		const int maxNumOfEmps, empNotFound;
    };
    I can't figure out how to instaniate empList to maxNumOfEmps and also to instantiate maxNumOfEmps to 100 and empNotFound to -1.
    I can't instantiate them in the constructor because they are constant and not in the class either. Major help needed.

    I tried this for instantiating the object in the constructors, which would work in Java (I think), but not in C++
    Code:
     EmpArys::EmpArys()
    {
    empArys[maxNumOfEmps];
    }
    Thanks, I greatly appreciate the help.
    Last edited by gflores; 08-17-2004 at 10:26 PM.

  2. #2
    Registered User axon's Avatar
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    Mt. Prospect, IL
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    2,572
    well, objects in java are a bit different that in c++. In Java you have low level types: int, char, but you also have Objects: Integer, String and so on.

    In your case, you cannot just make an object of type EmpArys=null, you need you constructor, set all the object's variables.

    some entropy with that sink? entropysink.com

    there are two cardinal sins from which all others spring: Impatience and Laziness. - franz kafka

  3. #3
    Registered User
    Join Date
    Jul 2004
    Posts
    98
    Code:
    EmpArys::EmpArys()
    {
    empArys[maxNumOfEmps];
    }
    I change it like this:
    Code:
    class newEmpArys::EmpArys()   //define another class
            : EmpArys
    {
           empArys[maxNumOfEmps];
    }

  4. #4
    Registered User hk_mp5kpdw's Avatar
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    Jan 2002
    Location
    Northern Virginia/Washington DC Metropolitan Area
    Posts
    3,794
    Const data members need to be set in a class' initializer list. This is the only place they can be set upon creation of an instance of a particular object. The following modifications will allow you to create an EmpArys object with a value for maxNumOfEmps that you specify when instantiating an object. You can specify a value or not in which case a default value of 100 will be given. empNotFound gets set to -1.
    Code:
    class EmpArys
    {
    public:
            EmpArys(const int maxEmps);
            ~EmpArys();
            int findEmp(int pSocSecNbr);
            Employee getEmp(int pSocSecNbr);
            bool addEmp(Employee pEmp);
            bool delEmp(int pSocSecNbr);
            string toString();
            string getPayList(Tax pTaxTable);
    private:
            Employee* empList;
            int empCount;
            const int maxNumOfEmps, empNotFound;
    };
    
    EmpArys::EmpArys(const int maxEmps = 100) : maxNumOfEmps(maxEmps), empNotFound(-1)
    {
        // Dynamically allocate a chunk of memory to hold maxNumOfEmps Employees
        empList = new Employee[maxNumOfEmps];
    }
    
    EmpArys::~EmpArys()
    {
        // Clean up dynamically allocated memory
        delete [] empList;
    }
    ...
    ...
    ...
    EmpArys a1;         // maxNumOfEmps for object a1 gets default value of 100
    EmpArys a2(200);    // maxNumOfEmps for object a2 gets value of 200
    
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

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