Bug in K&R second edition?

Question

Here's something that looks like a bug to me, however I am confused that my observation does not seem to pop up anywhere else on the internet, given the age and popularity of the book. Or maybe I am just bad at searching or it is not a bug at all.

I am talking about the "print out the longest input line" program from chapter one. Here's the code:

#include <stdio.h>
#define MAXLINE 1000 /* maximum input line length */

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

/* print the longest input line */
main()
{
    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)
        if (len > max) {
            max = len;
            copy(longest, line);
        }
    if (max > 0) /* there was a line */
        printf("%s", longest);
    return 0;
}

/* getline: read a line into s, return length */
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;
    }
    s[i] = '\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;
} 

Now, it seems to me that it should be lim-2 as opposed to lim-1 in the for condition of getline. Otherwise, when the input is exactly of maximum length, that is 999 characters followed by '\n', getline will index into s[MAXLINE], which is out of bounds, and also all kinds of horrible things might happen when copy is called and from[] does not end with a '\0'.

Answer 1

I think you're confused somewhere. This loop condition:

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

Ensures that i is never greater than lim - 2, so in the maximum-length case, i is lim-1 after the loop exits and the null character is stored into that last position.

Answer 2

In the case of 999 non-\n characters followed by a \n, c never equals \n. When the for loop exits, c is equal to the last non-newline character.

So c != '\n' and doesn't enter the block that does i++ so i never goes out of bounds.

Answer 3

When the input is of length 999 and is followed by \n, value of limit is 1000 and the value of lim -1 will become 999 and the loop test condition i < lim -1 will become false when i becomes 998. For i < 999, c == \n never be true and hence array s will indexed to s[999] and not s[1000]