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structure and typedef

This is a discussion on structure and typedef within the C Programming forums, part of the General Programming Boards category; Hi, I have seen the following code and was surprised Code: #include <stdio.h> int main() { typedef struct name name1; ...

  1. #1
    Registered User
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    Feb 2012
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    structure and typedef

    Hi,
    I have seen the following code and was surprised
    Code:
    #include <stdio.h>
    
    int main()
    {
       typedef struct name name1;
    
       struct name
       {
           int i;
           char array[10];
       };
     name1 name2;
     name2.i = 13;
     printf("%d",name2.i);
     return 0;
    }
    In the line typedef struct name name1, the name structure is not yet defined and why the compiler is not giving any error. Also i cannot define a structure within a structure that is cannot reference itself but i can define a pointer to reference itself. Can someone please explain me what is the logic involved in all these things.

    Thanks and regards,
    Satya

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    14,185
    typedef merely renames things; it does not require any information about what that thing is. As long as that thing gets defined, everyone's happy.

    As to the second question, of course a structure cannot contain a copy of itself, because that copy must then contain another copy of itself, and that copy must then contain another copy of itself, .... A pointer is a different type of data, and does not cause an infinite loop as the above would.

  3. #3
    and the hat of Marriage Rodaxoleaux's Avatar
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    A structure inside of the same structure. Thinking about it hurts my head...
    Code:
    struct foo
    {
        struct foo _foo;
    }
    
    
    struct foo bar;
    bar._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo._foo = bar;
    Oh... that's beautiful.
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