Do you use bit fields?

[Alan Rooks]

I have used bitfields in many applications using sets of binary flags. However,
I came across one type of problem in which their use is inconvenient. The
program was a maze generator, and i needed 4 bits for each cell, with bit i
stating whether there was a wall in direction i (i = up, down, left, right).
The problem came up when I had an int (or enum) variable, call it j,
specifying the direction number, and i wanted to check for the wall:

#define	UP	0
#define	DOWN	1
#define	LEFT	2
#define	RIGHT	3

    switch(j) {

    case UP:
	iswall = maze[x][y].up;
	break;

    case DOWN:
	iswall = maze[x][y].down;
	break;

    case LEFT:
	iswall = maze[x][y].left;
	break;

    case RIGHT:
	iswall = maze[x][y].right;
	break;
    }

... when i could do it this way if maze[x][y] was just an int:

    iswall = (maze[x][y] & (1 << j)) != 0;

... or even simpler,

#define	UP	1
#define DOWN	2
#define	LEFT	4
#define	RIGHT	8

    iswall = (maze[x][y] & j) != 0;

... which is nice and simple. The problem exists because i want to be
able to index my bits, and C bitfields don't give you a way to do that.
Like I said however, i have found them very useful in other applications.

Alan Rooks at the University of Waterloo; ...!utzoo!watmath!watrose!ajrooks