I am trying my hand at C by implementing Conway's game of Life.
I am trying to dynamically build two grids (int matrices), one for the current and one for the next generation, so after I determine what the next generation looks like, I just swap pointers.
At first I tried hopelessly to define the pointer to the grid like int * grid, which you cannot subscript with a second set of brackets like [][] because - obviously - the first set of brackets returns an int.
I also tried something like int * grid[HEIGHT][WIDTH], but this gives problems assigning one pointer like this to another. (And in fact, I have no idea what this really does in memory!)
In my naïve hopefulness, I thought the following could work after stumbling across double pointers. The program compiles, but fails when running on the line indicated. (In Windows, I get no more detail other than that the Problem Event Name is APPCRASH).
DISCLAIMER: This is not the actual program, just a proof of concept for the problem.
#include <stdio.h>
#include <stdlib.h>
int HEIGHT = 20;
int WIDTH = 20;
int ** curr_gen; // Current generation
int ** next_gen; // Next generation
/* Entry Point main */
int main(int argc, char** argv) {
// Allocate memory for the grids
curr_gen = malloc(sizeof (int) * WIDTH * HEIGHT);
next_gen = malloc(sizeof (int) * WIDTH * HEIGHT);
curr_gen[0][0] = 0; //<< PROGRAM FAILS HERE
// Release heap resources
free(curr_gen);
free(next_gen);
return 0;
}
A common way to do this is described in http://c-faq.com/aryptr/dynmuldimary.html