分配二维数组的一维并返回

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;

Answer 2

Your are mixing arrays and pointers, these are not the same.

uint16_t coord[][2];

is an incomplete type, since you didn't define one dimension. You would fixe that dimension by using an initializer. It seems that you are not really familiar with that concept, so better you'd warm up with a one dimensional one:

uint16_t line[] = { 1, 2, 3 };

would give it three elements.