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, tab_pos = 0;
	for (i = 0; (c = getchar()) != EOF; i++) {
		if (c == '\t') {
			if (i >= initial_col) {
				for (j = 0; j < (tab_stop - tab_pos); j++) {
					putchar(' ');
				}
				tab_pos = 0;
			} else {
				putchar('\t');
				i += tab_stop;
			}
		} else {
			putchar(c);

			if (c == '\n') {
				tab_pos = 0;
				i = 0;
			} else {
				tab_pos++;
				tab_pos %= tab_stop;
			}
		}
	}
}