Problem with vectors and classes

This is a discussion on Problem with vectors and classes within the C++ Programming forums, part of the General Programming Boards category; Hi guys. I'm having a problem with getting a vector to fill with my location class here is the code: ...

  1. #1
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    Problem with vectors and classes

    Hi guys. I'm having a problem with getting a vector to fill with my location class here is the code:
    Code:
    #include<iostream>
    #include<vector>
    using namespace std;
    class location
    {
        public:
        int x,y;
        static int id;
        char fill;
        location(int x2, int y2, char a)
        {
    	x  = x2;
    	y = y2;
    	fill = a;
    	id++;
        }
    };
    class board
    {
        public:
        board()
        {
    	vector<location>board(361, new location(0,0,'+'));
        }
    };
    void makeBoard()
    {
        
    }
    int main(int argc, char **argv)
    {
        makeBoard();
        return 0;
    }
    Could someone tell me how to fix this? I know the program doesn't really do anything but I get some compiling errors.

    axel

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    If you post compiler errors we can help you much more easily.
    Code:
    vector<location>board(361, new location(0,0,'+'));
    Perhaps you need a space there?
    Code:
    vector<location> board(361, new location(0,0,'+'));
    [edit]
    And you don't need new there.
    [/edit]
    dwk

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  3. #3
    Frequently Quite Prolix dwks's Avatar
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    Code:
    id++;
    You can't do that, given id is a static variable and that statement is in a non-static function.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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  4. #4
    Frequently Quite Prolix dwks's Avatar
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    BTW, you can call your constructor arguments the same as the class variables, and access the class variables using the this pointer:
    Code:
    class location
    {
        public:
        int x,y;
        static int id;
        char fill;
        location(int x2, int y2, char a)
        {
    	x  = x2;
    	y = y2;
    	fill = a;
    	id++;
        }
    };
    ->
    Code:
    class location
    {
        public:
        int x,y;
        static int id;
        char fill;
        location(int x, int y, char fill)
        {
    	this->x  = x;
    	this->y = y;
    	this->fill = fill;
    	id++;
        }
    };
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


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  5. #5
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    Quote Originally Posted by dwks
    Code:
    id++;
    You can't do that, given id is a static variable and that statement is in a non-static function.
    That's incorrect:
    Code:
    class Location
    {
    public:
    	static int id;
    
    	int x,y;
    	char fill;
    
    	Location(int x2, int y2, char a)  //non-static function
    	{
    		x  = x2;
    		y = y2;
    		fill = a;
    		id++;  //static member
    	}
    };
    
    int Location::id = 1;
    
    int main()
    {
    	Location myL(10, 20, 'x');
    	cout<<myL.id<<endl;
    
    	return 0;
    }
    Last edited by 7stud; 04-08-2006 at 01:08 PM.

  6. #6
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    >> vector<location>board(361, new location(0,0,'+'));

    You don't want the new there. You may be confused by Java (or not). Since the vector holds location objects, you just need to pass a location object for it to use to initialize its elements.

    The problem you will have is that id will be incorrect because you only increment it in the regular constructor but not the copy constructor (which is compiler generated in this case). When you create three instances in the vector with that code, all three will be copy constructed and so id will not get incremented. The solution depends on what you really want to do with id.

    Also note that your class is called board, so you don't want the vector variable to be called board as well.

  7. #7
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    vector<location>board(361, new location(0,0,'+'));
    Also, i don't see this variable declared in the class declaration so this is nothing but a local variable there i presume, which in this case is doing nothing.

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