Question

I’m on to K&R’s Exercise 1-18

Write a program to remove trailing blanks and tabs from each line of input, and to delete entirely blank lines.

This is what I’ve came up with so far

#include <stdio.h>

#define MAXLINE 1000

int getline(char line[], int maxline);
void copy(char to[], char from[]);

int main () {

    int len;
    char line[MAXLINE];

    while (getline(line, MAXLINE) > 0) {
            printf("%s", line);
    }
    return 0;
}


int getline(char s[], int lim) {
    int c, i, lastNonBlankIndex;
    lastNonBlankIndex = 0;

    for (i=0; i < lim - 1 && (c = getchar()) != EOF && c != '\n'; ++i) {

        if (c != ' ' && c != '\t') {
            lastNonBlankIndex = i + 1;

        } 

        s[i] = c;
    }

    if (i != lastNonBlankIndex) {
        i = lastNonBlankIndex;
        c = '\n';
    }

    if (c == '\n') {
        s[i] = c;   
        ++i;
    }
    s[i] = '\0';
    return i;
}

The second part sounded hard, as I wasn’t sure what I should return if the line only has blanks or tabs. After all, if I return 0, it will halt the getline() calling. Would this be where I should set up a #define, such as ALL_BLANKS.

Anyway, to actual main question, is this a correct way to remove trailing blanks and tabs from lines? I ran a few inputs through, and it seemed to work. However, if I copy and paste text with newlines into the CL, it appears all strung together. And when I type a line into the CL and push enter, it automatically prints it. Should I be building an array of lines, and then looping through and printing them when done ?

Answer 1

Your code looks correct, but I think it would be better if you separate the operations of reading a line from stdin and stripping the line of trailing whitespace (decoupling). Then you can use the unmodified getline from the book (code reuse) and won’t have the problem of halting on returning 0.

And if you are interested in other solutions, the CLC-wiki has an almost complete list of K&R2 solutions.

#include <stdio.h>
#define MAXLINE 1024

int getline(char s[], int lim);

main()
{
    int i, len;
    char line[MAXLINE];

    while ((len = getline(line, MAXLINE)) > 0) {
        i = len - 2;
        while (i >= 0 && (line[i] == ' ' || line[i] == '\t'))
            --i;
        if (i >= 0) {
            line[i+1] = '\n';
            line[i+2] = '\0';
            printf("%s", line);
        }
    }
    return 0;
}

This is the category 1 solution I wrote some time ago. getline is as on page 28 of the book. It might be nicer to put the removal of whitespace in a separate function rstrip, but I leave this as an exercise for the reader.