K&R 1.9 \\ exceeding the scope of an array?

Question

I'm having a difficult time understanding this function:

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;
}

I will try to explain my doubts with an example input of 0123456789\n (for a total of 11 characters).

In this example lim=10 and s[] is set to line[10] (from the declaration of the calling argument of getline).

When the loop has finished running trhough ++i these are the values: i==9, s[0]==0, ..., s[9]==9, c=='\n' (because getchar executes as part of the check condition).

Then the if checks positive and s[9] is set to '\n' while i is raised to 10.

Finally, s[10] is set to '\0', but s[10] doesn't exist!

Also, s[] later prints to 012345678 with the value of s[9] being reserved for one between '\n' and '\0'.

Where is '\0' being stored? I know it's there somewhere because later another function makes use of it to check for the end of the array.

Answer 1

Because of the chcek i<lim-1, if lim is 10, i will never become 9 inside for loop, it can reach a max value of 8, before the condition check fails.

After i becomes 9, the first part of the for loop condition check fails, and the control comes out of loop [without executing getchar() for that iteration).

So, upto s[8] is read and at s[9], the \0 is stored.