The C Programming Language, exercise 1-20 (DETAB input).

ex-1-20-detab.c

// Exercise 1-20. Write a program detab that replaces tabs in the input with
// the proper number of blanks to space to the next tab stop. Assume a fixed
// set of tab stops, say every n columns. Should n be a variable or a symbolic
// parameter?


// $ gcc -std=c99 -Wall -pedantic -L./lib -o devel devel.c -lmyline
// $ LD_LIBRARY_PATH=./lib ./devel <<< $'Li\tnu\tx\t\t!'
// len 39, line Li--------nu--------x----------------!

#include <stdio.h>
#include "lib/line.h"

#define MAXLEN 200      // Max input length allowed.
#define TABSIZE 8       // 8 spaces for each tab size.

int detab(char line[], int len);

int main(void)
{
    int len;
    char line[MAXLEN];

    while ((len = get_line(line, MAXLEN)) > 0) {
        len = detab(line, len);
        fprintf(stdout, "len %d, line %s", len, line);
    }

    return 0;
}

int detab(char line[], int len)
{

    int i, j;

   int pos_dst;
   int pos_src;

    i = 0;
    while (line[i] != '\0') {
        if (line[i] == '\t') {
            pos_dst = len + TABSIZE - 1;
            j = len;
            while (j > i) {
                pos_src = j;
                //printf("len %d, j %d, pos_src %d, pos_dst %d\n", len, j, pos_src, pos_dst);
                line[pos_dst] = line[pos_src];
                --pos_dst;
                --j;
            }
            while (pos_dst >= i) {
                line[pos_dst] = '-';
                --pos_dst;
            }
            len += TABSIZE - 1;
        }
        ++i;

    }

    return len;
}