Looking for help with pointer idea.

This is a discussion on Looking for help with pointer idea. within the C++ Programming forums, part of the General Programming Boards category; Well, I don't really know how to explain this other than show you so that is what I'll do. Code: ...

  1. #1
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    Question Looking for help with pointer idea.

    Well, I don't really know how to explain this other than show you so that is what I'll do.

    Code:
    int* a = new int(1000);
    int* b = a;
    
    delete a; a = 0;
    I know that doesn't make any sense, but what I am wanting to do is that when a is freed b is automatically set to NULL also.

    I am also wanting to maintain the pointer syntax for the most part so I don't end up with another class that is unreadable. I also need to have it work on multiple levels. So basically
    Code:
    int* a = new int(1000);
    int* b = a;
    int* c = b;
    //etc etc
    I want c and b to be set to null when a is freed.

    I have been thinking about this for several hours, but I have yet to come up with anything that lets me maintain the regular syntax.

    - I don't care about allowing directly newing or deleteing the data as a function for this is fine
    - I want to maintain the * and -> to access the data for getting/setting

    I am hoping someone here can give me some insight/ideas on how to achieve this. I am very grateful for any assistance. Thank you.

  2. #2
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Raigne
    I know that doesn't make any sense, but what I am wanting to do is that when a is freed b is automatically set to NULL also.
    The solution is to use a std::tr1::shared_ptr instead of a raw pointer. (Or in the absence of a TR1 implementation, boost::shared_ptr.)

    EDIT:
    Actually, if only a has ownership while b (and c) does not, then a could be a std::tr1::shared_ptr while b (and c) would be a std::tr1::weak_ptr (or boost::weak_ptr, as the case may be).
    Last edited by laserlight; 01-07-2009 at 12:19 AM.
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  3. #3
    Beginner leiming's Avatar
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    About the second question, using:

    int* &b = a;
    int* &c = b;

  4. #4
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by leiming
    About the second question, using:

    int* &b = a;
    int* &c = b;
    That will only work if b (and c) will never be bound to another pointer.
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  5. #5
    Beginner leiming's Avatar
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    Quote Originally Posted by laserlight View Post
    That will only work if b (and c) will never be bound to another pointer.
    I just try writting some codes to reach it:
    Code:
    #include <iostream>
    using namespace std;
    
    class myintpointer{
    	public:
    		myintpointer(){
    			p2 = 0;
    			p = 0;
    		}
    		myintpointer(int* p){
    			this->p = p;
    			p2 = this;
    		}
    		operator int* (){
    			if (p2==this)
    				return p;
    			else
    				return *p2;
    		}
    		int* operator = (int *p){
    			this->p = p;
    			p2 = this;
    		}
    		myintpointer* operator = (myintpointer *p){
    			p2 = p;
    		}
    	private:
    		int *p;
    		myintpointer *p2;
    };
    
    int main(){
    	myintpointer a = new int;
    	myintpointer b, c;
    	*a = 1000;
    	c = b;
    	b = a;
    	cout << *a << " " << *b << endl;
    	delete a;
    	c = new int(2000);
    	b = c;
    	cout << *c << " " << *b << endl;
    	return 0;
    }
    I hope it helps.

  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by leiming
    I just try writting some codes to reach it:
    What do you mean? Your original suggestion seems pretty clear, just that it has a limitation that might not be relevant. (And it shares with Raigne's original code the disadvantage of having to do manual memory management.)
    Last edited by laserlight; 01-07-2009 at 02:01 AM.
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  7. #7
    Beginner leiming's Avatar
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    Quote Originally Posted by laserlight View Post
    What do you mean? Your original suggestion seems pretty clear, just that it has a limitation that might not be relevant. (And it shares with Raigne's original code the disadvantage of having to do manual memory management.)
    I mean if that shall work when b and c are bound to another pointer, this is the only way I can find.

    It has no other meanings. And because English is not my native language; if there are something I misunderstand, I say sorry for that.

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