Exercise 5.12

Page 118

Extend entab and detab to accept the shorthand entab -m +n to mean tab stops every n columns, starting at column m. Choose convenient (for the user) default behavior.

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

#define DEFAULT_TAB_STOP 4
#define DEFAULT_INITIAL_COL 0

int main(int argc, char *argv[])
{
	unsigned tab_stop = DEFAULT_TAB_STOP;
	unsigned initial_col = DEFAULT_INITIAL_COL;

	int val;
	while (--argc > 0) {
		if (isdigit(argv[argc][1])) {
			val = atoi(argv[argc] + 1);
			switch (argv[argc][0]) {
			case '-':
				initial_col = val;
				break;
			case '+':
				tab_stop = val;
				break;
			}
		}
	}

	int c, i, j;
	int tab_pos = 0, nb = 0;
	for (i = 0; (c = getchar()) != EOF; i++) {
		++tab_pos;
		tab_pos %= tab_stop;

		if (c == ' ' && i >= initial_col) {
			nb++;
			if (tab_pos == 0) {
				if (nb > 1) {
					putchar('\t');
				} else {
					putchar(' ');
				}
				nb = 0;
			}
		} else {
			for (j = 0; j < nb; j++) {
				putchar(' ');
			}

			nb = 0;
			if (c == '\n') {
				tab_pos = 0;
				i = 0;
			}

			putchar(c);
		}
	}
}