Structure Declaration

This is a discussion on Structure Declaration within the C Programming forums, part of the General Programming Boards category; Hi There, can some one tell me how to declare a function with a pointer to a structure, i know ...

  1. #1
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    Oct 2012
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    Structure Declaration

    Hi There,

    can some one tell me how to declare a function with a pointer to a structure, i know how to do it with the structure outside of the main function but unclear how to do it with the structure inside.

    Code:
    void function();
    
    void main()
    {
        struct hello{
                        int goodbye;
                        int evening;
                       }
    hello.goodbye = 1;
    function();
    
    }
    
    void function()
    {
    printf("%d", hello->goodbye);
    }
    basically how do i declare the functions

    thanks

  2. #2
    qny
    qny is offline
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    Code:
    /* First, define the structure outside functions.
    ** Just the definition, I'm not talking about variables (objects)
    ** of the structure at this time */
    struct hello {
        int goodbye;
        int evening;
    };
    
    /* now the prototype, using pointers to the structure */
    void function(struct hello *);
    
    /* The main() function */
    int main(void) {
        struct hello hello = {1}; /* initialization; all unmentioned members are initialized to 0 */
        hello.evening = 42; /* assignment ot a specific member */
        function(&hello); /* call the function */
        return 0;
    }
    
    void function(struct hello *p) {
        printf("%d\n", p->goodbye);
    }

  3. #3
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    Long Beach, CA
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    Well, if you declare struct hello inside main, it will only be visible inside main. Any other function wishing to use that type can't, it doesn't know what such a structure looks like. Thus, as far as I can tell, your question is irrelevant.

    If you do want to declare it inside main, you need a semicolon after the struct declaration. Then, declare your variable as usual. Alternatively, you can squeeze the variable definition into the struct definition, but I think it would make your code harder to read.
    Code:
    int main(void)
    {
        struct hello {
            int goodbye;
            int goodbye;
        };
        struct hello foo, *bar;  // foo is a variable of type 'struct hello', bar is type 'pointer to struct hello'
        // or
        struct hello {
            int goodbye;
            int goodbye;
        } foo, *bar;  // same as above, but struct and variables in one statement -- I do not recommend this
        ...
        return 0;
    }
    Also, it's int main(void), and return an int at the end, usually 0. Read this: FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com.

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