Single-malloc char** allocation.

foo.c

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

#define N (3)

const size_t offset = sizeof(char *) * N,
	length = (sizeof(char *) + sizeof(char) * N) * N;

int main(int argc, char **argv) {
	char **foo = (char **)malloc(length);
	int i, j;

	for (i = 0; i < N; ++i) {
		foo[i] = (char *)(foo + offset + i * N);
	}

	/* usage */

	for (i = 0; i < N; ++i)
		for (j = 0; j < N; ++j)
			foo[i][j] = 'a' + i * j;

	for (i = 0; i < N; ++i) {
		for (j = 0; j < N; ++j)
			printf(" %c", foo[i][j]);
		putchar('\n');
	}
		

	return 0;
}