Two dimensional C arrays – care and feeding

C arrays are a little hard to grasp by those of us raised on the Cocoa API, because most of the really convenient stuff (like an array object being able to keep track of its own size) just isn’t there in straight C.  I went into using C arrays, in order to interact with OpenGL, with absolutely no knowledge whatsoever (a common theme of this site!) of how to even use malloc.

Why would you want to use two-dimensional arrays anyway?  In my case, although I’ve written a fair few functions where e.g. a two-dimensional grid of points is mapped to a long one-dimensional array, and I’ve simply remembered what the dimensions of the grid were when accessing the information, sometimes this is simply too much for my poor brain to understand. In this situation I’m forced to represent things as a multidimensional array in order to get the concepts down in a way which works.  I might, therefore, have one array which represents all of the values of the x dimension, containing a series of arrays which represent the y dimension; so the point in the grid at (5, 13) is retrieved by getting the 13th value from the 5th subarray in the parent array.

Fortunately there are people who are much cleverer than me who have come up with a way of handling two-dimensional C-arrays.  Unfortunately I have forgotten the attribution.  However, I had to go forum-diving to find this and I think that it might be helpful for us inexperienced types to have a more easily-searched solution.  If I find the original source again, I will provide a link.

One similar implementation was found here

//make a 2d array of floats
 
float** Make2DFloatArray(long lengthMainArray, long lengthSubArray) {
    float **newArray = (float **) malloc(lengthMainArray * sizeof(float *));
    *newArray = malloc(lengthMainArray * lengthSubArray * sizeof(float));
    for (int i = 0; i < lengthMainArray; i++) {
        newArray[i] = *newArray + i * lengthSubArray;
    }
    return newArray;
}
 
//release a 2d array of floats
 
void free2DFloatArray (float **arrayToFree) {
    free(*arrayToFree);
    free(arrayToFree);
}
 
//access a value in the 2d array
 
float theFloatIWant = my2DFloatArray[indexInMainArray][indexInSubArray];

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