Question

(This question is answered earlier but solution is not working or I am not able to understand it!!)

I want to use large size matrix of say 2^16*2^16.How to do that?
Here is code I used with malloc:

// nrows=2^16
// ncols=2^16

 int **a_matrix = (int**) malloc (nrows *sizeof(int*));

for (int i=0; i<nrows;i++)
a_matrix[i]=(int*) malloc (ncols *sizeof(int));
enter code here

now when I try to access a_matrix[55000][55000] its giving segmentation fault

I increased stack size to unlimited(with some commands) but still its not working.:(
Is there any other way to do it?

Edit: I just want to store 1/0 so even bool will work.But in that case also same problem!

Answer 1

If you just want to store booleans, using a packed bit-array would reduce the storage far enough that it would probably work. In C++, you would use a std::vector<bool> or a std::bitset; in C,

#include <stdint.h>

unit32_t (*a_matrix)[1<<11] = malloc((1 << 16)*sizeof *a_matrix);

gives you (if the malloc call doesn’t fail) a pointer to an array of 2^16 arrays of 2^16 bits. To access a bit, use

((a_matrix[row][column >> 5]) >> (column & 0x1F)) & 1

It’s probably best to make that a function

int bit_at(int row, int col) {
    return ((a_matrix[row][col >> 5]) >> (col & 0x1F)) & 1;
}

or maybe a macro.