# OpenGL Read data from file, to display

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Hi, im having a problem with how to read in vertex and index data from an XML file and display via OpenGL. Previously I hade been doing this (not reading data from xml) // A cube // { posX, posY, posZ, normX, normY, normZ } static const float vertices[24][6] = { { ... }, { ... }, { etc... } }; const int nVertices = 24; static const int indices[36] = { 0, 1, 2, ... }; const int nIndices = 36; // draw cube using Begin, End, Normal3*, Vertex3* glBegin( GL_TRIANGLES ); for ( int i=0; i<nIndices; i++ ) { glNormal3fv( vertices[ indices[i] ] ); glVertex3fv( vertices[ indices[i] ] ); } glEnd(); However I am now reading in from an XML file which reads (this is a small one): <mesh name="tri"> <vertexArray count="3"> -1.0 0.0 -1.0 0.0 -1.0 0.0 1.0 0.0 -1.0 0.0 -1.0 0.0 0.0 0.0 1.0 0.0 -1.0 0.0 </vertexArray> <indexArray count="3" primitive="triangles"> 0 1 2 </indexArray> </mesh> I can read XML no problem. It's just this is done in a class function and I'm trying to read the data into: float vertices , which is a member of the class (it wasn't previously). But i dont know how to put the data into vertices because I can't preset the array with how many vertices there are (vertices[nVertices][6] a no-no) Can anyone help me ? (I hope I've described this well enough)

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std::vector allows you to "push" onto it's own list. This means you don't need to know the number of vertices beforehand as you can just keep dropping them onto the vector.

typedef std::vector<float> Vertex;Vertex VertexList;// You can create one for each axis if you like.

Then as you're reading them in, it helps to be able to differentiate between the different dimensions you're using. (So if it reads x, y, x, y, x, y.. or x, x, x, y, y, y:

If I read your correctly it's going x, y, z, x, y, z..
So Vertex[0] = x, Vertex[1] = y, Vertex[2] = z and then back to x.

// Obviously not exactly what you should put, this is just the general idea.while(!EndOfXMLData){   VertexData = XMLReader.GetVertex();                           VertexList.push_back(VertexData);}// To Recall your data is the exact same way as an array.glBegin( GL_TRIANGLES );for ( int i=0; i<nIndices; i++ ){glNormal3fv( VertexList[i] );glVertex3fv( VertexList[i] );}glEnd();

Like I said, this isn't exact, but should give you the general idea of where to go with it :)

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you can use realloc

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