CODEWITHSUNDEEP
cmultidimensional-array
Zwiebel
Zwiebel

Reputation: 1615

How to dynamic allocate a two dimensional array

I would like to make a two dimensional array in C.

For example, I make an int type variable named place like this:

int *place;

I have a game, which have variables like rows, and columns. I would like my place variable to be a two dimensional array, with dynamic allocation of its rows and columns (for the max size of the array), which would look like this in the "normal" declaration:

place[rows][columns];

but I don't know how to do it with the dynamic allocation.

I would do it like this for one-dimensional arrays:

place = (int*) malloc (levels * sizeof(int));

but I don't know how to do this with 2D arrays.

Edit:

How I can rewrite this for char instead of int?

I have tried to just overwrite the ints with chars, but it doesn't work.

Upvotes: 4

Views: 7827

Answers (3)

akaHuman
akaHuman

Reputation: 1352

You need to do the following to allocate arr[x][y] of type int dynamically: 

 int i = 0;
 int **arr = (int**)calloc(x, sizeof(int*));
 for(i = 0; i < x; i++)
      arr[i] = (int *) calloc(y, sizeof(int));

The idea is to first create a one dimensional array of pointers, and then, for each array entry, create another one dimensional array.

Upvotes: 0

asheeshr
asheeshr

Reputation: 4114

You could use a single 1d array as a 2d array by some smart indexing :

Allocate memory :

place = (int*) malloc(rows * columns * sizeof(int));

To access place[i][j], use i and j as :

place[ i*columns + j] = value ;

Upvotes: 0

Daniel Fischer
Daniel Fischer

Reputation: 183978

Let place be a pointer to arrays,

int (*place)[columns] = malloc(rows * sizeof *place);

That gives you a contiguous block of memory (good for locality) that you can simply access with

place[i][j] = whatever;

Upvotes: 10

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