Classes and Destroyed Instances

This is a discussion on Classes and Destroyed Instances within the C++ Programming forums, part of the General Programming Boards category; If I created 5 instances of a class... IE: Code: class Enemy{blah blah} Enemy inst1; Enemy inst2; Enemy inst3; Enemy ...

  1. #1
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    Classes and Destroyed Instances

    If I created 5 instances of a class...

    IE:
    Code:
    class Enemy{blah blah}
    
    Enemy inst1;
    Enemy inst2;
    Enemy inst3;
    Enemy inst4;
    Enemy inst5;
    ...And I destroyed instances 1 3 and 4, but I use those instances in my coding...

    IE:
    Code:
    draw_object(inst1);
    draw_object(inst2);
    draw_object(inst3);
    draw_object(inst4);
    draw_object(inst5);
    ...how would I keep the program from executing functions using destroyed instances?

  2. #2
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    If you use pointers you could set the objects to NULL when you destroy them, then check to see if an object is not NULL before you use it. Or in your deconstructor you could set a flag like bDead = true; and check the value of bDead before you use an object.

  3. #3
    Registered User major_small's Avatar
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    if you're not using pointers, the only way to really destroy an object is to let it run out of scope. in that case, you'd get a compile error when you hit the statements with them in it. if you're talking dynamic memory, you're talking new/delete, and this is how you could do it (essentially what Sfpiano just told you about the pointers):
    Code:
    #include<iostream>
    
    struct test     //I'm using this in place of your classes
    {
            int i;  //just some dummy data
    };
    
    int main()
    {
            test a;                 //instantiate test
            test*b=new test;        //create a test pointer, and initilize it
            a.i=0;                  //fill in the dummy data for a
            b->i=1;                 //fill in the dummy data for b
            delete b;               //delete b
            b=0;                    //make the pointer point to nothing (NULL)
    
            std::cout<<a.i;         //output a
            if(b!=0)                //check if b pointer is pointing to a test
            {
                    std::cout<<'\n'<<b->i;  //if it is, print it
            }
            std::cout<<std::endl;   //either way put a newline & flush the stream
            return 0;               //return 0
    }
    Last edited by major_small; 07-12-2005 at 10:57 PM.
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  4. #4
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    Thanks

    Thanks for the help...I thought of something similar to that (it involved pointers anywayz) but was much more complicated. So thanks again!

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