declaring arrays with visual C++ toolkit 2003

This is a discussion on declaring arrays with visual C++ toolkit 2003 within the C++ Programming forums, part of the General Programming Boards category; I am trying to create an array based off of a argument in one of my functions. Here is my ...

  1. #1
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    declaring arrays with visual C++ toolkit 2003

    I am trying to create an array based off of a argument in one of my functions. Here is my code:

    Code:
    void Engine::PrimitiveEnd(CUSTOMVERTEX* buffer, int vertnumber)
    {
        CUSTOMVERTEX verts[vertnumber];
        
        for (int i = 0; i < tempverts.size(); ++i)
        {
            verts[i].x = tempverts[i].x;
            verts[i].y = tempverts[i].y;
            verts[i].z = tempverts[i].z;
        }
        
        buffer = verts;
    }
    These are the errors I get:

    Engine.cpp(159) : error C2057: expected constant expression
    Engine.cpp(159) : error C2466: cannot allocate an array of constant size 0
    Engine.cpp(159) : error C2133: 'verts' : unknown size


    But I only get this using the visual C++ toolkit 2003, but the GCC compiler does not give this error (but for reaons I can't use GCC).

    How would I declare an array of "unknowen" size than.

  2. #2
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    EDIT: Nevermind, I just glanced at it. I don't know.
    Last edited by durban; 11-02-2005 at 08:19 PM.
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    Actaully I get no error on that part. I only get the errors on this line:

    CUSTOMVERTEX verts[vertnumber];


    sorry for leaving that part out.

  4. #4
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    What is tempverts?
    -"What we wish, we readily believe, and what we ourselves think, we imagine others think also."
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    temp verts is declared globaly in the class like this:

    vector<CUSTOMVERTEX> tempverts;

    The user puts data into tempverts with anouther function than the function above (first post) gives the user the final result.

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    The reason I ask is: You're letting the user set the length of verts but you'r looping through tempverts.size() which I don't get. Say I entered 1 for vertnumber and the size of tempverts is 12 it would generate an error. for(int i=0; i<vertnumber; i++) should be your loop.
    -"What we wish, we readily believe, and what we ourselves think, we imagine others think also."
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    oh about that, well if I put tempverts.size() for the size of the array, I get the same errors. I supose using the size of tempverts would be better but I get the same errors.


    EDIT: once I get this to work, I will change that back to my original code wich is what you said.
    Last edited by Rune Hunter; 11-02-2005 at 08:29 PM.

  8. #8
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    yea that's what I was about to suggest, I dunno then. www.bitcomet.com . Download Microsoft Visual Studio 2005
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  9. #9
    semi-colon generator ChaosEngine's Avatar
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    Quote Originally Posted by Rune Hunter
    Actaully I get no error on that part. I only get the errors on this line:

    CUSTOMVERTEX verts[vertnumber];


    sorry for leaving that part out.
    you cannot (statically) declare an array with a variable that is not a compile-time constant. Visual studio is quite correct to pull you up on this. I believe gcc has an extension which allows this but it is not standard.

    you need to do
    Code:
    CUSTOMVERTEX* verts = new CUSTOMVERTEX[vertnumber];
    but then you need to remember to delete verts.

    I suggest a vector
    Code:
    vector<CUSTOMVERTEX> verts(vertnumber);
    "I saw a sign that said 'Drink Canada Dry', so I started"
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    ahh ha. I see the * in there makes all the difference. That worked perfectly.

    That was perfect timing, right before I am going to bed, thanks.

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    >> buffer = verts;

    That line does nothing, since you are passing buffer by value. If it worked in your original code, you'd be saving a pointer to a local variable, which is also bad. If you use new as the solution, and change buffer to be passed by reference, then as long as you delete buffer later in the calling code you are fine.

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    ok lets say I return verts, but I can't delete it cause the return exits the function. Would that be fine?

    This is my new code:

    Code:
    CUSTOMVERTEX* Engine::PrimitiveEnd()
    {
        CUSTOMVERTEX* verts = new CUSTOMVERTEX[tempverts.size()];
        
        for (int i = 0; i < tempverts.size(); ++i)
        {
            verts[i].x = tempverts[i].x;
            verts[i].y = tempverts[i].y;
            verts[i].z = tempverts[i].z;
            verts[i].color = tempverts[i].color;
        }
        
        return verts;
    }
    The code works 100% but I want to know is that safe or is there something wrong with the way I did it.

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    It is a memory leak if you don't delete [] it somewhere else in your code. The function that calls PrimitiveEnd should save the return value and delete [] it when it is done with it, or pass the pointer value to some other code that will eventually delete [] it.

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    So if I use the function like this:

    Code:
    CUSTOMVERTEX* verts1 = eng.PrimitiveEnd();
    and just call:

    Code:
    delete verts1;
    in my clean up section, it should be fine?

  15. #15
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    You'll notice I kept putting delete [] in my response (with the brackets). I did that for a reason. Once you figure out what that reason is, then, yes, it should theoretically avoid any memory leaks.

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