Thread: pointers?

  1. #1
    Registered User tu_user's Avatar
    Join Date
    Jan 2004

    Post pointers?

    What is the diference btw a pointer & a pointer variable?

    I mean I was confused by the following statement while reading an article,

    int x, y;

    *yPtr = 7;

    yPtr =&y;

    *yptr and yPtr is confusing.

  2. #2
    Confused Magos's Avatar
    Join Date
    Sep 2001
    basically, instead of storing a value, a pointer stores an adress to a variable that stores a value.

    Here you set the value yPtr points at
    *yPtr = ...

    Here you set the adress to where yPtr should point. You should not use an arbitrary number here but rather get the address of a variable through the & operator ( &myInt ).
    yPtr = ...

    There is a pointer tutorial on this site:

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  3. #3
    Been here, done that.
    Join Date
    May 2003

    Re: pointers?

    As Magos said, pointers store an address to a variable.

    In your examples:

    yPtr =&y;
    store the address of y into yPtr.
    You can now reference y or *yPtr as the same value.

    *yPtr = 7;
    7 is stored in the location that yPtr points to. IOW y is set to 7.

    By the way, you must specify yPtr:
    int x, y, *yPtr;
    This tells the compiler that yPtr will store an address.
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  4. #4
    Hardware Engineer
    Join Date
    Sep 2001

    Pointers can be confusing at first.

    But, pointers are used alot, so you'll get plenty of practice.

    One thing that confused me at first was that the asterisk (*) has a different meaning in a declaration than in an assignment:

    int *yPtr = &y; // This is OK (* means yPtr is a pointer, not dereferenced)
    *yPtr = &y; // Wrong (Address of y assigned to whatever yPtr "points to")
    yPtr = &y; // This is OK (Address of y assigned to yPtr)
    *yPtr = x; // This is OK (* means "dereference". x is assigned to whatever yPtr "points to")

  5. #5
    Registered User major_small's Avatar
    Join Date
    May 2003
    I always found it easier to think about it like this:
        int x=10;           //integer x
        int y=10;           //integer y
        int*xptr=new int;   //pointer to new integer
        int*yptr=&y;   //pointer to new integer (same as yptr=&y)
        *xptr+=5;   //add 5 to xptr's copy of x (xptr only points to the value)
        *yptr+=5;   //add 5 to y (yptr points to the address of y)
        delete xptr; //because it points to a newly allocated int-size chunk of memory
        *xptr=0; //point it to nothing
    now when you print it out, it looks liek this:
    x:     10
    y:     15
    *xptr: 15
    *yptr: 15
    xptr:  0x...
    yptr:  0x...
    it's like in a function, when you use the ampersand (&) in the calling of the function to change that variables value in main as well... actually, that's exactly what it is, but I don't want to try to confuse you anymore...
    Last edited by major_small; 01-20-2004 at 04:55 PM.
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  6. #6
    Registered User tu_user's Avatar
    Join Date
    Jan 2004

    Thumbs up

    thanku v m.

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