Jagged Arrays

by Jii Yoo
…
Note
|
Writing

A jagged array, also known as an irregular array, is a type of multidimensional array. The difference is that in jagged array, each element (itself an array) can have a different length producing rows of jagged edges.

*arr[4] 
            ---------------------
arr[0] ---> | 0 | 1 | 2 |
arr[1] ---> | 6 | 4 |
arr[2] ---> | 1 | 7 | 6 | 8 | 9 |
arr[3] ---> | 5 |
            ----------------------

If regular multidimensional array is used instead of a jagged array for the above structure, it would look like this.

arr[4][5]
            ---------------------
arr[0] ---> | 0 | 1 | 2 | _ | _ |
arr[1] ---> | 6 | 4 | _ | _ | _ |
arr[2] ---> | 1 | 7 | 6 | 8 | 9 |
arr[3] ---> | 5 | _ | _ | _ | _ |
            ----------------------
        
_ => NULL or any other default values

Jagged arrays are useful for storing data with different length, such as sparse matrices. They could be more useful than multidimensional arrays where members have the same length, because only needed spaces are used; no space is wasted.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
	const unsigned SIZE = 4;
	int *arr[SIZE];

	unsigned sz[] = {3, 2, 5, 1};

	for(int i=0; i<SIZE; ++i)
		arr[i] = (int *)malloc(sizeof(int) * sz[i]);

	arr[0][0] = 0;
	arr[0][1] = 1;
	arr[0][2] = 2;

	arr[1][0] = 6;
	arr[1][1] = 4;

	arr[2][0] = 1;
	arr[2][1] = 7;
	arr[2][2] = 6;
	arr[2][3] = 8;
	arr[2][4] = 9;

	arr[3][0] = 5;

	for(int i=0; i<SIZE; ++i) {
		printf("Array row #%d: ", i+1);
		for(int j=0; j<sz[i]; ++j) {
			printf("%d ", arr[i][j]);
		}
		printf("\n");
	}

	for(int i=0; i<SIZE; ++i)
		free(arr[i]);

	return 0;
}

The above code produces the following result.

Array row #1: 0 1 2 
Array row #2: 6 4 
Array row #3: 1 7 6 8 9 
Array row #4: 5
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