malloc 2d array code example

Example 1: c malloc for 2d array

#include <stdlib.h>

	int **array;
	array = malloc(nrows * sizeof(int *));
	if(array == NULL)
		{
		fprintf(stderr, "out of memory\n");
		exit or return
		}
	for(i = 0; i < nrows; i++)
		{
		array[i] = malloc(ncolumns * sizeof(int));
		if(array[i] == NULL)
			{
			fprintf(stderr, "out of memory\n");
			exit or return
			}
		}

Example 2: double pointer malloc in c

char *x;  // Memory locations pointed to by x contain 'char'
char **y; // Memory locations pointed to by y contain 'char*'

x = (char*)malloc(sizeof(char) * 100);   // 100 'char'
y = (char**)malloc(sizeof(char*) * 100); // 100 'char*'

// below is incorrect:
y = (char**)malloc(sizeof(char) * 50 * 50);
// 2500 'char' not 50 'char*' pointing to 50 'char'