pointers and memory

This is a discussion on pointers and memory within the C++ Programming forums, part of the General Programming Boards category; howdy, im learning pointer and memory management from a book. ive been playing with this C++ stuff for a few ...

  1. #1
    In The Light
    Join Date
    Oct 2001
    Posts
    598

    pointers and memory

    howdy,
    im learning pointer and memory management from a book. ive been playing with this C++ stuff for a few months now but when i start reading and typing the sample code for the pointers i can not get a handle on what is going on. for example:

    ~~~~~~~~~~~code~~~~~~~~~~~~~~~
    #include <iostream.h>
    #include <iomanip.h>

    int main()
    {
    int stuff[3][4] = {{11, 22, 45, 23},
    {33, 67, 28, 45},
    {98, 4, 71, 90}};

    int *ip;
    int(*ip4)[4]; //WHAT IS THIS FOR?
    int i, j;

    ip4 = stuff;
    ip =(int *) stuff; //POINTER NOT TO AN ARRAY??

    cout<<"Storage of date: "<<endl'
    for(i=0;i<4; i++)
    cout<<ip[i];
    cout<<endl;

    cout<"Matrix concept: "<<endl;
    for(i=0; i<3; i++)
    {
    for(j=0; j<4; j++)
    {
    cout<<*(*(ip4 =i) + j)<<" "; //WHAT IS THIS DOING
    }
    cout<<endl;
    }
    getchar(); //freezes the screen
    return 0;
    }
    ~~~~~~~~~~~~~code~~~~~~~~~~~~~~~~~

    sorry about the format i couldnt figure out how to put @#&%$ code tags on this thing.

    thanks
    M.R.

  2. #2
    Registered User
    Join Date
    Dec 2001
    Posts
    421

    Lightbulb

    int(*ip4)[4]; //WHAT IS THIS FOR?
    That statement is declaring a variable called ip4, which is a pointer to an array of 4 integers.

    ip =(int *) stuff; //POINTER NOT TO AN ARRAY??
    ip is a pointer to an integer. stuff is a 2 dimensional array containing 3 x 4 integers. when you refer to 'stuff' in your code' you are doing the same as saying '&stuff[0][0]' ... and since this is an address containing and integer value, you are able to point an integer pointer to it.

    cout<<*(*(ip4 =i) + j)<<" "; //WHAT IS THIS DOING
    hrm.. interesting statement... are you sure you didn't type it wrong?? It should be ip4 + i shouldn't it?? It's using i to offset the address of the pointer (ie... to reference array 1, 2 and 3 in the 2d stuff array), and using j to loop through the items in that array. it's just using pointers and dereferencing rather than array indexes...

    getchar(); //freezes the screen
    this doesn't freeze the screen... it waits for user input (one character).... used a lot for the 'press a key to continue' type functionality.

    hope this helps.
    U.
    Quidquid latine dictum sit, altum sonatur.
    Whatever is said in Latin sounds profound.

  3. #3
    Registered User rmullen3's Avatar
    Join Date
    Nov 2001
    Posts
    330
    Heh, I was wondering about that = in there...

  4. #4
    Registered User rmullen3's Avatar
    Join Date
    Nov 2001
    Posts
    330
    Code:
    #include <stdio.h>
    #include <iostream.h>
    #include <iomanip.h>
    
    int main()
    {
    	int stuff[3][4] = { {11, 22, 45, 23},
    						{33, 67, 28, 45},
    						{98, 4, 71, 90} };
    	int *ip;
    	int(*ip4)[4]; //WHAT IS THIS FOR?
    	int i, j;
    	
    	ip4 = stuff;
    	ip =(int *) stuff; //POINTER NOT TO AN ARRAY??
    
    	cout<<"Storage of date: " << endl;
    	for(i=0;i<4; i++)
    		cout << ip[i];
    	
    	cout << endl;
    
    	cout << "Matrix concept: " << endl;
    
    	for(i=0; i<3; i++) {
    		for(j=0; j<4; j++) {
    			cout << *(*(ip4 +i) + j) << " "; //WHAT IS THIS DOING
    		}
    		cout << endl;
    	}
    
    	getchar(); //freezes the screen
    	return 0; 
    }
    a bit more legible.

  5. #5
    In The Light
    Join Date
    Oct 2001
    Posts
    598
    sorry folks,
    the = is a suposed to be a +. I have to add that getchar(); so when i move this code from linux back to borland it wont disapear before it confuses the he__ out of me.

    thanks for the explaination. ill digest this thing and keep forging ahead.

    Thanks
    M.R.

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