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Arrays and Pointers

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Join Date: Mar 2008

Posts: 40

Reputation: midimatt is an unknown quantity at this point

Solved Threads: 2

midimatt

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Light Poster

Arrays and Pointers

Dec 19th, 2008

Hello again everyone,

Having a really annoying problem using pointers and arrays at the moment,

i'm trying to store a 4x4 matrix as a an array of 16 floats.

so i declare my array like so

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	float array1[] =	{1.0f,0.0f,0.0f,0.0f,
						0.0f,1.0f,0.0f,0.0f,
						0.0f,0.0f,1.0f,0.0f,
						50.0f,0.0f,0.0f,1.0f};
	float array1[] =	{1.0f,0.0f,0.0f,0.0f,
						0.0f,1.0f,0.0f,0.0f,
						0.0f,0.0f,1.0f,0.0f,
						50.0f,0.0f,0.0f,1.0f};

i then pass this into an object using my set function like so

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baseNode->setPositionMatrix(array1);

code for setPositionMatrix()

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void sceneObject::setPositionMatrix(float* nPositionMatrix)
{
	positionMatrix = nPositionMatrix;
}
void sceneObject::setPositionMatrix(float* nPositionMatrix)
{
	positionMatrix = nPositionMatrix;
}

it doesnt throw up any errors, but when it draws with the new matrix it doesnt draw properly, so i investigated and it seems that positionMatrix only holds the first value from nPositionMatrix which is being passed in.

and i'm really not sure what to do.

thanks in advance for anyone who can help me out here.
-Midi

Last edited by midimatt; Dec 19th, 2008 at 7:12 pm.

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Join Date: Nov 2008

Posts: 397

Reputation: StuXYZ is a glorious beacon of light

Solved Threads: 72

StuXYZ

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Posting Whiz

Re: Arrays and Pointers

Dec 19th, 2008

Looks like you are coping the pointer BUT not coping the array.
[This is often called weak-copy].
What happens is the memory for array1 is overwritten with something else and you have a copy of the memory location.
You need something like this

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void sceneObject::setPositionMatrix(float* nPositionMatrix)
{
       if (!positionMatrix)
	  positionMatrix = new float[16];
        for(int i=0;i<16;i++)
          positionMatrix[i]=nPositionMatrix[i]; 
}
void sceneObject::setPositionMatrix(float* nPositionMatrix)
{
       if (!positionMatrix)
	  positionMatrix = new float[16];
        for(int i=0;i<16;i++)
          positionMatrix[i]=nPositionMatrix[i]; 
}

Note: You can use memcpy but the loop is self explanatory.

If postionMatrix is defined float positionMatrix[] you will not need the if
construct. If it is not you must remember to delete [] it later

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