Question

I try to dynamically allocate one dimension of a two dimensional array. The array is declared as follows:

uint16_t coord[][2];

I only need to allocate the rows, the number of coordinates.
Over google I found enough code to allocate both of the dimensions, starting from:

uint16_t **coord;

I am not sure if I can still declare the array as above. Do I need to do:

uint16_t *coord[2]; 

or not?

I also need to return the array (the pointer to it) from the allocating function so other functions can access the array like this:

foo = coord[4][0];
bar = coord[4][1];

What’s the correct way to return the allocated array?

Answer 1

According to the clockwise/spiral rule, the following declaration:

uint16_t *coord[2];

is an array of two pointers, which seems to be not what you want. However you can use this instead:

uint16_t (*coord)[2];

You can allocate memory for it like this:

coord = malloc(num_entries * sizeof(uint16_t[2]));

Now you can access it as a normal multi-dimensional array:

coord[0][0] = 1;
coord[0][1] = 2;
coord[1][0] = 3;
coord[1][1] = 4;