When does this program return 0

Question

The following function is to return the length of a line that is entered through keyboard. But its saying that (The C Programming language K & R) it will return the length of the line, or zero if end of file is encountered. But when I analyzed with my basic knowledge in C at least it is returning the length of the line till EOF. So when does it returns 0. Or my understanding is wrong. Can anybody clarify me ?

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 think your analysis is correct. It will return the number of chars read until EOF or newline. — harald, Jun 24 '13 at 11:25
@noufal, only if the file is empty or the last charecter in the file is a newline. — harald, Jun 24 '13 at 14:03

score 2 · Answer 1 · answered Jun 24 '13 at 11:22

2

You analyzed the program correctly.

But when I analyzed with my basic knowledge in C at least it is returning the length of the line till EOF

-> It will return 0 when the line is empty

answered Jun 24 '13 at 11:22

Tom van der Woerdt

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... but isn't it just returning the length of the line, then? Why mentioning this case as something special? – undur_gongor Jun 24 '13 at 11:23
It returns the length of the line, yes, as seen in the quote. – Tom van der Woerdt Jun 24 '13 at 11:24
Together with noufal, I'm wondering why the quote doesn't just say "it will return the length of the line". Or, why not "... or 1 if there is an EOF after one character in a line"? – undur_gongor Jun 24 '13 at 11:26
@undur_gongor Because then it wouldn't be a quote anymore – Tom van der Woerdt Jun 24 '13 at 11:27
@TomvanderWoerdt if `EOF` is at the end a line, it should return the number of characters in that line ? – noufal Jun 24 '13 at 12:56

score 2 · Accepted Answer · answered Jun 24 '13 at 11:28

2

When there's nothing, EOF will be there e.g. in case of Empty line, c==EOF and you have entered a condition in your for loop that (c=getchar())!=EOF. Thus i won't change and when it will be returned after execution of return i;, it will return 0

I hope this helps.

answered Jun 24 '13 at 11:28

Shumail

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suppose if I am entering like `qwertyEOF`, it should return the number `6` ? right ? – noufal Jun 24 '13 at 12:45
No. it will return 9. Read this for explanation of EOF in detail: http://stackoverflow.com/questions/3061135/can-we-write-an-eof-character-ourselves p.s please Vote UP for answer and accept it. it encourages infact ;) – Shumail Jun 24 '13 at 12:47
CTRL + D ? As per my knowledge, EOF by definition "is unequal to any valid character code" and there's no such character. in DOS, it used to be CTRL + Z but not now. – Shumail Jun 24 '13 at 13:01
Entering EOF at end of line won't make it read EOF infact, it will treat it as normal characters. – Shumail Jun 24 '13 at 13:03
1

I did understand your point. BTW I didn't mean entering `E, O, F` from keyboard. – noufal Jun 24 '13 at 14:05
Accept answer Please then. – Shumail Jun 24 '13 at 14:28

score 0 · Answer 3 · 2013-06-24T17:07:36.690

0

If the line is empty, it will return 0.

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

First, You set i=0;. If ((c=getchar())==EOF), the for loop won't run and i won't be incremented. The situation is the same when the first character is a \n (in this case i will be incremented later)

edited Jun 24 '13 at 17:07

answered Jun 24 '13 at 11:23

when the first character is `\n`, it will return `1`, not `0` – noufal Jun 24 '13 at 17:01
@noufal Yes, You're right. i will be incremented later outside the loop. – Jun 24 '13 at 17:07

scarecrow · Answer 4 · 2013-06-24T11:46:25.623

0

one of the conditions in the for loop is (c=getchar())!=EOF. So when the line is empty, ie. c==EOF at the first instance itself, it doesnt enter the loop. Hence i won't get incremented and it returns 0.

edited Jun 24 '13 at 11:46

answered Jun 24 '13 at 11:24

scarecrow

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if I enter the `EOF` at the end of a line, then ? – noufal Jun 24 '13 at 12:41
@noufal can you explain a bit? – scarecrow Jun 24 '13 at 14:14
I got now what was wrong with my understanding. If nothing is there, `EOF` will be there over and over again – noufal Jun 24 '13 at 16:59

When does this program return 0

4 Answers4