"The C Programming Language", 2nd edition, Kernighan and Ritchie

Answer to Exercise 1-16, page 30

Solutions by Richard Heathfield and "386sx"

Revise the main routine of the longest-line program so it will correctly print the length of arbitrarily long input lines, and as much as possible of the text. 

/* This is the first program exercise where the spec isn't entirely
 * clear. The spec says, 'Revise the main routine', but the true
 * length of an input line can only be determined by modifying
 * getline. So that's what we'll do. getline will now return the
 * actual length of the line rather than the number of characters
 * read into the array passed to it.
 */

#include <stdio.h>

#define MAXLINE 1000 /* maximum input line size */

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

/* print longest input line */
int main(void)
{
  int len;               /* current line length */
  int max;               /* maximum length seen so far */
  char line[MAXLINE];    /* current input line */
  char longest[MAXLINE]; /* longest line saved here */

  max = 0;

  while((len = getline(line, MAXLINE)) > 0)
  {
    printf("%d: %s", len, line);

    if(len > max)
    {
      max = len;
      copy(longest, line);
    }
  }
  if(max > 0)
  {
    printf("Longest is %d characters:\n%s", max, longest);
  }
  printf("\n");
  return 0;
}

/* getline: read a line into s, return length */
int getline(char s[], int lim)
{
  int c, i, j;

  for(i = 0, j = 0; (c = getchar())!=EOF && c != '\n'; ++i)
  {
    if(i < lim - 1)
    {
      s[j++] = c;
    }
  }
  if(c == '\n')
  {
    if(i <= lim - 1)
    {
      s[j++] = c;
    }
    ++i;
  }
  s[j] = '\0';
  return i;
}

/* copy: copy 'from' into 'to'; assume 'to' is big enough */
void copy(char to[], char from[])
{
  int i;

  i = 0;
  while((to[i] = from[i]) != '\0')
  {
    ++i;
  }
}



Chris Sidi, however, was not convinced - he thought this answer was "too easy", so he checked with bwk, who agreed. Chris writes: "Looks like Mr. Kernighan meant for "main routine" in Exercise 1-16 to refer to function main(), saying your solution of modifying getline() is "too easy." :) (Though I think your solution shouldn't be removed from the Answers web site, just complimented with another one that only modifies main())"

Cue Mr "386sx", riding to the rescue on a white horse... 

/* Exercise 1-16 */

#include <stdio.h>

#define MAXLINE 20

int getline(char s[], int lim);
void copy(char to[], char from[]);

int main(void)
{
    char line[MAXLINE];
    char longest[MAXLINE];
    char temp[MAXLINE];
    int len, max, prevmax, getmore;
    
    max = prevmax = getmore = 0;
    while((len = getline(line, MAXLINE)) > 0)
    {
        if(line[len - 1] != '\n')
        {
            if(getmore == 0)
                copy(temp, line);
            prevmax += len;
            if(max < prevmax)
                max = prevmax;
            getmore = 1;
        }
        else
        {
            if(getmore == 1)
            {
                if(max < prevmax + len)
                {
                    max = prevmax + len;
                    copy(longest, temp);
                    longest[MAXLINE - 2] = '\n';
                }
                getmore = 0;
            }
            
            else if(max < len)
            {
                max = len;
                copy(longest, line);
            }
            prevmax = 0;
        }
    }
    if(max > 0)
    {
        printf("%s", longest);
        printf("len = %d\n", max);
    }

    return 0;
}

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

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

    if(c == '\n')
    {
        s[i] = c;
        ++i;
    }
    else if(c == EOF && i > 0)
    {
        /* gotta do something about no newline preceding EOF */
        s[i] = '\n'; 
        ++i;
    }
    s[i] = '\0';
    return i;
}

void copy(char to[], char from[])
{
    int i;

    i = 0;
    while((to[i] = from[i]) != '\0')
        ++i;
}



Back to index




You are visitor number - call again soon!