pointer problem

This is a discussion on pointer problem within the C Programming forums, part of the General Programming Boards category; Hi, I'm relatively new to this (still working my way through the textbooks!) and I'm having a bit of trouble ...

  1. #1
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    pointer problem

    Hi, I'm relatively new to this (still working my way through the textbooks!) and I'm having a bit of trouble with the following pointer:


    unsigned long int step, win_sum;
    float lacu_index, cal_lacu();
    long int win_size;
    unsigned char *store,*win_inside ;
    long address1,address2;
    fpos_t *img_start, *win_start;
    img_start = &address1;
    win_start = &address2;


    I've been going over this for hours now and I still dunno whats up. Any suggestions would be really greatful.

  2. #2
    ATH0 quzah's Avatar
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    Do you know the basics of pointers? Pointers are just like other variables. They store values. The values that pointers store are the addresses of other variables. Other than that, they're exactly the same. So what you do is use the "address of" operator ( & ) to get the address of a variable, so you can stick that address in a pointer.

    Pointers also let you "dereference" them, using the asterix, to get the contents of whatever they point at.

    What's happening here is that you're taking the address of two longs and sticking those addresses into two different variables, of type "pointer to fpos_t".

    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    Quote Originally Posted by gaulter
    Hi, I'm relatively new to this (still working my way through the textbooks!) and I'm having a bit of trouble with the following pointer:


    unsigned long int step, win_sum;
    float lacu_index, cal_lacu();
    long int win_size;

    unsigned char *store,*win_inside ;
    long address1, address2;
    fpos_t *img_start, *win_start;

    img_start = &address1;
    win_start = &address2;

    I've been going over this for hours now and I still dunno whats up. Any suggestions would be really greatful.
    I may be wrong, but it looks like you have pointers that are supposed to be pointing to variables of type "fpos_t", but it's actually pointing to a long. I don't see "fpos_t" defined anywhere, though...
    Last edited by Krak; 01-27-2005 at 03:46 PM.

  4. #4
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    fpos_t is a typedef - an alias for a datatype.

    For most file systems fpos_t is an unsigned long (or whatever datatype will the max possible bytes in a file)

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