Thread: another question on pointers

  1. #1
    Registered User
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    another question on pointers

    i have come across **pointer_name before and as i decided to have a couple hours break from the poker game im writing i thought i would experiment.
    what is the difference between this
    Code:
    void double_it(int *p_number)
    {
        *p_number *= 2;
    }
    
    void add_three(int *p_num)
    {
        *p_num += 3;
        double_it(p_num);
    }
    int main()
    {
        int x = 1;
    
        add_three(&x);
        printf("x = %d\n", x);
        return 0;
    }
    and this
    Code:
    void double_it(int **p_number)
    {
        **p_number *= 2;
    }
    
    void add_three(int *p_num)
    {
        *p_num += 3;
        double_it(&p_num);
    }
    int main()
    {
        int x = 1;
    
        add_three(&x);
        printf("x = %d\n", x);
        return 0;
    }
    both give the correct answer of 8 (or at least the one i was expecting)

    i don't see the purpose of writing int **number when *number will do.
    coop

  2. #2
    C++ Witch laserlight's Avatar
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    Not useful here. Useful when you need to assign to a pointer within a function such that it is changed in the caller, e.g., dynamic memory allocation. That is, when an out parameter is a pointer itself.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    ok thanks i think that is probably where i saw it in an example of memory request

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