too many *'s

This is a discussion on too many *'s within the C Programming forums, part of the General Programming Boards category; ok i just want to double check this there is a function which reads out an array as Code: Func ...

  1. #1
    Wanabe Laser Engineer chico1st's Avatar
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    too many *'s

    ok i just want to double check this

    there is a function which reads out an array as

    Code:
    Func ((void **)&Array)
    but this function is in a library inside another function and i need to pass 'array' out

    So this would look like

    Code:
    int otherFunc((void **)Array){
            Func ((void **)&Array)
            ... 
            other stuff
            ...
            return 0;
    }
    Which I would call like:
    Code:
    otherFunc((void **)&Array)
    Is this right... i understand the idea of pointers and addresses but i dont like it when they get mixed with arrays.

  2. #2
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    Errm... what?

    What are the functions and variables declared as and what are you trying to do?

  3. #3
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    Quote Originally Posted by chico1st View Post
    ok i just want to double check this

    there is a function which reads out an array as

    Code:
    Func ((void **)&Array)
    [/CODE]
    This is wrong. You're passing the address of the temporary representing the pointer to the array, and passing it to Func.

    You're also not following naming conventions.

    A function that takes a void ** should take an array of void pointers as its argument.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

  4. #4
    Wanabe Laser Engineer chico1st's Avatar
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    Quote Originally Posted by robwhit View Post
    Errm... what?

    What are the functions and variables declared as and what are you trying to do?
    Func ((void **)&Array)
    Is a function that I have to use from a library which reads data from some hardware that I have

    All i want to do is pass on that data as a pointer since i need to access it from another program

    This function (otherFunc) will be part of a library which I need.

  5. #5
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    doesn't Func have a return type?

  6. #6
    Wanabe Laser Engineer chico1st's Avatar
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    ok yes int Func

  7. #7
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    When you have an & in the prototype, that means a reference. And you don't use typecasts in the prototype ((void **)). But references are C++. This is the C board. Are you sure you have the prototype of the function and the right board?
    Last edited by robwhit; 05-20-2008 at 06:13 PM.

  8. #8
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    I think that's the call. Otherwise it might look like:
    Code:
    int Func (void *&Array)

  9. #9
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    ok, if it's the call, then what's the prototype?

  10. #10
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    >ok, if it's the call, then what's the prototype?
    Actually you raise an interesting question, because the following isn't even a valid function declaration:
    Code:
    int otherFunc((void **)Array){
    That what the original post looks like.

  11. #11
    Wanabe Laser Engineer chico1st's Avatar
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    Quote Originally Posted by swoopy View Post
    >ok, if it's the call, then what's the prototype?
    Actually you raise an interesting question, because the following isn't even a valid function declaration:
    Code:
    int otherFunc((void **)Array){
    That what the original post looks like.
    So what am I supposed to do?
    i am hopelessly confuzed now.

    And I am supposed to be writing in C, if i did c++ by accident then thats bad

  12. #12
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    Can you post the correct (compilable without errors) prototype of Func() - perhaps you can dig out the header file that has the prototype and post the ACTUAL function prototype.

    I wrote a bit of code like this:
    Code:
    int func(void **p);
    
    int main()
    {
       void *ptr;
       
       func(&ptr);
       return 0;
    }
    It compiles, but doesn't link since I don't have a "func" somewhere.

    --
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  13. #13
    Wanabe Laser Engineer chico1st's Avatar
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    Code:
    Int32 func(void** Array);
    if you were to be passing the value for ptr into main what would it look like?
    Code:
    int func(void **p);
    
    int main(*ptr)
    { 
       func(ptr);
       return 0;
    }
    OR
    Code:
    int func(void *p);
    
    int main(*ptr)
    { 
       func(&ptr);
       return 0;
    }
    Last edited by chico1st; 05-21-2008 at 09:24 AM.

  14. #14
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    >Int32 func(void** Array);
    How is the array you want to pass to this function declared? Is it:
    Code:
    int *num_array;
    Or:
    Code:
    int **num_array;
    Or:
    Code:
    int num_array[10];
    Or:
    Code:
    int *num_array[10];
    Or is it actually a void **:
    Code:
    void **array;
    Or something else?

  15. #15
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    Yes, one of those is right - it depends A LOT on what the function actually expects. It is impossible to say from just seeing the prototype of a function whether it expects the address of a void pointer [and whether it should be a void pointer that points to some valid memory, or if the function just sets the pointer to something within the function], or it expects the address of (for example) an array.

    Without either source of func, or the documentation of func, it's not possible for us to say what it does.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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