variable definitions

This is a discussion on variable definitions within the C Programming forums, part of the General Programming Boards category; I had an exam today and ran into something i have never seen before. Question went something like this: int ...

  1. #1
    Registered User dan20n's Avatar
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    variable definitions

    I had an exam today and ran into something i have never seen before.
    Question went something like this:

    int **x ();

    what is the type of *x?

    Any ideas?
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  2. #2
    Devil's Advocate SlyMaelstrom's Avatar
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    x is either a function that returns a pointer to a pointer to an int or it's just a regular pointer to pointer to int that your teacher decided would be acceptable to put parenthesis next to that don't contain an initialization value. The type of *x would be a pointer(in otherwords, it holds a memory address). Does this suit you better?
    Code:
    int** x();
    Code:
    #include <stdio.h>
    
    int foo = 2;
    int **x(); // this is the prototype you see
    
    int main()
    {
       printf("%i", **(x()));
       
       return 0;
    }
    
    int **x()
    {
       int* bar = &foo;
       int** baz = &bar;
       
       return baz;
    }
    Last edited by SlyMaelstrom; 06-06-2006 at 05:21 AM.
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  3. #3
    Registered User dan20n's Avatar
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    Ah yes, thank you for your reply. Im aware of these functions. I wrote the original post in haste because I was hoping for a quick answer as i cant find one. it bugging me big time.

    Ill reword the question:

    If i declare a _variable_ like this

    int **x ( );

    what is the type of *x?

    the word variable throwing me off here.. doesnt make sense to me, but that is how it was written in the test.
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  4. #4
    Devil's Advocate SlyMaelstrom's Avatar
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    As I wrote, declaring a variable like that... that is to say not a function, is illegal. If this was C++, it could be legal however, you'd have to intialize the variable in the parenthesis, such as
    Code:
    int **x(&y);
    This isn't C++, though, and as that currently stands, your linker will end up complaining about an undefined reference to x when you try to build.
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  5. #5
    Registered User dan20n's Avatar
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    I'm 99% sure it was in the ANSI C part of the test. But once reading it could be legal in C++ then it has put doubt in my mind. Well my answer was a pointer to an int, was a guess but anyways...

    Thanks for your time.
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    Stewie: Hm, the end result of a drunken back-seat grope-fest and a broken prophylactic?

  6. #6
    ATH0 quzah's Avatar
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    It's not a variable. It's a function prototype. You must be remembering the question wrong. You can't get "*x" for the code you've listed.

    Sly, your code is incorrect also, because your variable is not static, and as such, you're returning values which go out of scope when the function ends.


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  7. #7
    Devil's Advocate SlyMaelstrom's Avatar
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    Agreed, but I didn't want to pass an arguement which may confuse the OP. I suppose a global variable would be more proper.
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  8. #8
    and the hat of wrongness Salem's Avatar
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    > int **x ( );
    x is a function taking unspecified arguments, and returning a pointer to a pointer to int.
    Note that () means (...) in C, but (void) in C++

    > what is the type of *x?
    This makes no sense, since you can't dereference a function name

    I suppose you could do
    int *result = *x();
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  9. #9
    Registered User dan20n's Avatar
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    The question was small; I wrote it on my hand so I didn’t make a mistake. My self and my peers agree that it must have been a mistake in the wording, still waiting on confirmation from the lecturer. Thanks for your help though..
    Meg: Everybody! Guess what I am?
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  10. #10
    ATH0 quzah's Avatar
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    Quote Originally Posted by SlyMaelstrom
    Agreed, but I didn't want to pass an arguement which may confuse the OP. I suppose a global variable would be more proper.
    All you had to do is make your variables static:
    Code:
    int **x( void )
    {
        static int foo = 5;
        static int *bar = &foo;
        static int **baz = &bar;
        return baz;
    }

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

  11. #11
    Devil's Advocate SlyMaelstrom's Avatar
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    Yeah sure that works. From now on, I shall begin all posts I type when I haven't slept in a while with...

    ---zzz


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