how to pass 2 dimensional array if both dimensions are unknown at compile time

Question

what is this the correct way to pass 2 dimensional array of unknown size?

reprVectorsTree::reprVectorsTree(float tree[][], int noOfVectors, int dimensions)
<         


        

Answer 1

If the size is unknown, you can use a simple float *tree pointer to a 1D array. The syntax for turning to particular elements wouldn't be as of 2D arrays however:

reprVectorsTree::reprVectorsTree(float *tree, int noOfVectors, int dimensions)
{
    ...
    tree[ row_number * dimensions + column_number ] = 100.234;
}

In the calling code you will have something like this:

float d2array[ROWS][COLUMNS];
...
reprVectorsTree(&d2array[0][0], ROWS, COLUMNS);

updated

Consider the following example of different approaches of passing a 2D array:

#include 
#include 

float test[2][4] = 
{
   {3.0, 4.0, 5.0, 0},
   {6.0, 7.0, 8.0, 0}
};

void print(float *root, int rows, int columns)
{
   for (int row = 0; row < rows; ++row)
   {
      for (int col = 0; col < columns; ++col)
      {
         std::cout << root[row * columns + col ] << " ";
      }
      std::cout << std::endl;
   }
}

float *test2[2] = 
{
   &test[0][0],
   &test[1][0],
};

void print2(float **root, int rows, int columns)
{
   for (int row = 0; row < rows; ++row)
   {
      for (int col = 0; col < columns; ++col)
      {
         std::cout << root[row][col] << " ";
      }
      std::cout << std::endl;
   }
}

int main()
{
   print(&test[0][0], 2, 4);
   //print(test2, 2, 4); // doesn't work

   print2(test2, 2, 4);
   //print2(&test[0][0], 2, 4); // doesn't work
   //print2(&test[0], 2, 4); // doesn't work

   float **dynamic_array = (float **)malloc(2 * sizeof(float *));
   dynamic_array[0] = (float *)malloc(4 * sizeof(float));
   dynamic_array[1] = (float *)malloc(4 * sizeof(float));

   for (int row = 0; row < 2; ++row)
   {
      for (int col = 0; col < 4; ++col)
      {
         dynamic_array[row][col] = (float)(row * 4 + col);
      }
   }

   print2(dynamic_array, 2, 4);
   //print(dynamic_array, 2, 4); // doesn't work

   return 0;
}