struct arrays

This is a discussion on struct arrays within the C++ Programming forums, part of the General Programming Boards category; This is just a basic question. I've created a struct that needs to create mutliple instances, but of a constantly ...

  1. #1
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    struct arrays

    This is just a basic question. I've created a struct that needs to create mutliple instances, but of a constantly changing number.

    Grab number of objects from memory.
    Code:
    struct _NumOfObjects
    {
    	unsigned short Max;
    	unsigned short Num;	
    };
    _NumOfObjects * NumOfObjects = ( _NumOfObjects * ) OTNumAddy;
    Code:
    struct _Lengths
    {
    	float AX;
        float TrueBX;
        float ExtremeBX;
    	float AY;
        float TrueBY;
        float ExtremeBY;
    
        float dist; 
        float mx, my, mz;
    } Length[NumOfObjects->Num];
    I need to create an instance for each seperate object, but I get this error:

    error C2057: expected constant expression
    error C2466: cannot allocate an array of constant size 0

    Is there a way to do this without a constant? The num of objects changes quite frequently.

  2. #2
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    Are you using C or C++? In C++, you'd use a vector and specify the size when you create it. In C you could use malloc to dynamically allocate the array, or maybe use variable length arrays.

    BTW, technically you're not allowed to use any name that starts with an underscore followed by a capital letter.

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    I'm using C++ and I'm not very familiar with C functions =/

  4. #4
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    Quote Originally Posted by silentkarma View Post
    Code:
    _NumOfObjects * NumOfObjects = ( _NumOfObjects * ) OTNumAddy;
    WTF?

  5. #5
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    >> I'm using C++
    Ok, then:
    Code:
    std::vector<_Lengths> Length(NumOfObjects->Num);
    You have to make sure NumOfObjects is valid at that point, so I'm not sure making it global is a good idea, but hopefully you just did that as an example (or because you thought it was necessary for a struct -- it's not).

  6. #6
    In the Land of Diddly-Doo g4j31a5's Avatar
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    I think the problem is (like robwhit said), this:
    Code:
    _NumOfObjects * NumOfObjects = ( _NumOfObjects * ) OTNumAddy;
    What do you mean by it?
    ERROR: Brain not found. Please insert a new brain!

    “Do nothing which is of no use.” - Miyamoto Musashi.

  7. #7
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    Quote Originally Posted by g4j31a5 View Post
    I think the problem is (like robwhit said), this:
    Code:
    _NumOfObjects * NumOfObjects = ( _NumOfObjects * ) OTNumAddy;
    What do you mean by it?
    This is assigning a static memory address to this struct. This is for a game. I hope this makes sense. I'm doing calculations on each object and decided to use struct arrays. I figured this would be the easiest way because I can easily iterate through objects.

  8. #8
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    What is OTNumAddy?

  9. #9
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    Quote Originally Posted by Daved View Post
    What is OTNumAddy?
    const unsigned long OTNumAddy = 0x4BB206E2;

  10. #10
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    So NumOfObjects->Num is the value found at 0x4BB206E4. Do you have any idea how the compiler should know what will be at this address when you execute the code?

    --
    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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