Question about EOF.

Junky · 12-05-2009, 11:14 AM

I was reading a book about C programming, and I came across this program example:

Code:

#include <stdio.h>

int main() {
    int c;
    
    c = getchar();
    while (c != EOF) {
          putchar(c);
          c = getchar();
    }
}

Ok, the author was obviously explaining getchar() and putchar() :P
The author said that the type of c must be int, because EOF needs to fit inside too, along with all the other characters (in range from -128 to 127).

My question is: What is EOF? What do I type to get out of the loop?

quzah · 12-05-2009, 11:24 AM

EOF depends on your OS, shell or environment. Try either CTRL D or CTRL Z (no, no matter what any idiot that comes after me might say, it isn't CTRL C, ever).

Quzah.

Adak · 12-05-2009, 12:21 PM

From the CTRL D or CTRL Z Quzah mentioned, your compiler will probably give EOF a value of -1, if the file pointer is at the end of the file, or zero if it's not. CTRL Z and 0 or -1, was the standard from the DOS day.

It's still in use by Windows.

If you'd like to see CTRL Z in action, in Windows, open up a console (DOS) window.

type:
copy con Ancient.txt
Water, water, everywhere
And all the boards did shrink
Water, water, everywhere
Nor any drop to drink
<and press CTRL z>

You'll now have a file called Ancient.txt in your directory, with these few lines from The Rhyme of the Ancient Mariner

Junky · 12-06-2009, 04:41 AM

Tnx, it doesn't work for CTRL D/Z, but it works for CTRL C

One more question, but I don't want to open a new thread. The author said that you can do this:

Code:

#include <stdio.h>

int main() {
    char c;
    
    while((c = getchar()) != 'A') printf("Lol\n");
}

instead of this:

Code:

#include <stdio.h>

int main() {
    char c;
    
    c = getchar();
    while (c != 'A') {
           printf("Lol\n");
           c = getchar();
    }
}

But, why do both cases print "Lol\n" 2 times (in case I don't enter 'A')?

Adak · 12-06-2009, 05:24 AM

Quote:

Originally Posted by Junky

Tnx, it doesn't work for CTRL D/Z, but it works for CTRL C

Stop! On Windows it works. I just did it (again), on Windows XP, and I've done the same thing with CTRL z with nearly every version of Windows since Windows 3.1.

That's how I write up very small bat and text files.

I haven't tried it yet with Windows 7.

The posted program does the following:

First, it fills up the keyboard buffer with your keystrokes, until you hit 'A'. Each letter is also echo'd to stdout (usually the screen).

When the keyboard buffer is full, you will hear a beep every time you hit a key.

If you hit enter, it prints the Lol message, once for every key stroke, which allows the getchar() to empty the keyboard buffer. In my case, that's about 256 "Lol"'s.

If you still haven't hit 'A' key, then it waits for your next keystroke.

Quote:

But, why do both cases print "Lol\n" 2 times (in case I don't enter 'A')?

I'm not familiar with your system or compiler.

Junky · 12-06-2009, 05:33 AM

Windows XP, I'm working on Dev-C++.

Thanks, I think I understand now what does it actually do. I realized that it prints "Lol\n" 1 time if I just press "Enter", 2 times if I enter 1 character, 3 times if I enter 2 characters, although I still don't understand why does it print 2 times for 1 character.

Adak · 12-06-2009, 05:55 AM

if you mean it prints twice with every char you enter, then the answer is that the char you typed also has a char behind it, the newline, that was sent to the keyboard buffer when you hit the enter key.

the newline is also a char (until it becomes two char's (CR & LF, when opened as a text file).

Junky · 12-06-2009, 06:03 AM

Omg, you're right!!
Tnx

Junky · 12-07-2009, 08:20 AM

Ok, I'm getting really annoying with this, but I want to understand EOF completely.

Code:

#include <stdio.h>

int main() {
    int c,nl;
    
    nl = 0;
    while ((c = getchar()) != EOF) if (c == '\n') nl++;
    printf("%d\n",nl);
}

This is supposed to count lines. But I can't get to the 'printf' part, because, when I enter EOF (which is CTRL C), I get kicked out of the program. Does anyone know why?
(When I was testing it, I entered system("pause"), so that's not the problem).

BEN10 · 12-07-2009, 08:28 AM

Quote:

Originally Posted by Junky

Ok, I'm getting really annoying with this, but I want to understand EOF completely.

Code:

#include <stdio.h>

int main() {
    int c,nl;
    
    nl = 0;
    while ((c = getchar()) != EOF) if (c == '\n') nl++;
    printf("%d\n",nl);
}

This is supposed to count lines. But I can't get to the 'printf' part, because, when I enter EOF (which is CTRL C), I get kicked out of the program. Does anyone know why?
(When I was testing it, I entered system("pause"), so that's not the problem).

EOF is not CTRL-C, its CTRL-Z for Windows and CTRL-D for Linux. CTRL-C is some kinda interrput(which I'm not sure).

BEN10 · 12-07-2009, 08:33 AM

EOF explained
C99 defines EOF as a macro "which expands to an integer constant expression, with type int and a negative value, that is returned by several functions to indicate end-of-file".

Junky · 12-07-2009, 08:45 AM

I understand now. I was confused, because CTRL-Z gave me "^Z", but I just have to press enter. Tnx

dareck · 07-28-2010, 01:30 AM

I'm reading the same book on C programming as well. Though, Ctrl + Z dosen't seem to work for me. I'm using VS 2008 and windows 7 to run the code. I read somewhere that sometimes you'd have to use Ctrl + V first followed by Ctrl + Z. Is that the right way? Seems to have worked. Has anyone else tried it on windows 7?

dareck · 07-28-2010, 01:39 AM

and I had to press 'Enter' after Ctrl+v AND Ctrl+z

**laserlight** · 07-28-2010, 01:43 AM

Quote:

Originally Posted by dareck

I read somewhere that sometimes you'd have to use Ctrl + V first followed by Ctrl + Z. Is that the right way? Seems to have worked. Has anyone else tried it on windows 7?

Interesting, but that does not appear to work for me on Windows 7. I can confirm that CTRL+Z is the way to trigger EOF when writing to standard input at a command prompt for Windows. What I do is enter it on a new line.

12-05-2009, 11:14 AM	#1
Junky Registered User Join Date: Nov 2009 Posts: 14	Question about EOF. I was reading a book about C programming, and I came across this program example: Code: #include <stdio.h> int main() { int c; c = getchar(); while (c != EOF) { putchar(c); c = getchar(); } } Ok, the author was obviously explaining getchar() and putchar() :P The author said that the type of c must be int, because EOF needs to fit inside too, along with all the other characters (in range from -128 to 127). My question is: What is EOF? What do I type to get out of the loop?
Junky is offline

12-05-2009, 11:24 AM	#2
quzah +++ OK NO CARRIER Join Date: Oct 2001 Posts: 11,292	EOF depends on your OS, shell or environment. Try either CTRL D or CTRL Z (no, no matter what any idiot that comes after me might say, it isn't CTRL C, ever). Quzah. __________________ Hundreds of thousands of dipshits can't be wrong. Are you up for the suck?
quzah is offline

12-05-2009, 12:21 PM	#3
Adak Registered User Join Date: Sep 2006 Posts: 3,720	From the CTRL D or CTRL Z Quzah mentioned, your compiler will probably give EOF a value of -1, if the file pointer is at the end of the file, or zero if it's not. CTRL Z and 0 or -1, was the standard from the DOS day. It's still in use by Windows. If you'd like to see CTRL Z in action, in Windows, open up a console (DOS) window. type: copy con Ancient.txt Water, water, everywhere And all the boards did shrink Water, water, everywhere Nor any drop to drink <and press CTRL z> You'll now have a file called Ancient.txt in your directory, with these few lines from The Rhyme of the Ancient Mariner Last edited by Adak; 12-05-2009 at 12:52 PM.
Adak is offline

12-06-2009, 04:41 AM	#4
Junky Registered User Join Date: Nov 2009 Posts: 14	Tnx, it doesn't work for CTRL D/Z, but it works for CTRL C One more question, but I don't want to open a new thread. The author said that you can do this: Code: #include <stdio.h> int main() { char c; while((c = getchar()) != 'A') printf("Lol\n"); } instead of this: Code: #include <stdio.h> int main() { char c; c = getchar(); while (c != 'A') { printf("Lol\n"); c = getchar(); } } But, why do both cases print "Lol\n" 2 times (in case I don't enter 'A')?
Junky is offline

12-06-2009, 05:33 AM	#6
Junky Registered User Join Date: Nov 2009 Posts: 14	Windows XP, I'm working on Dev-C++. Thanks, I think I understand now what does it actually do. I realized that it prints "Lol\n" 1 time if I just press "Enter", 2 times if I enter 1 character, 3 times if I enter 2 characters, although I still don't understand why does it print 2 times for 1 character. Last edited by Junky; 12-06-2009 at 05:42 AM.
Junky is offline

12-06-2009, 05:55 AM	#7
Adak Registered User Join Date: Sep 2006 Posts: 3,720	if you mean it prints twice with every char you enter, then the answer is that the char you typed also has a char behind it, the newline, that was sent to the keyboard buffer when you hit the enter key. the newline is also a char (until it becomes two char's (CR & LF, when opened as a text file).
Adak is offline

12-06-2009, 06:03 AM	#8
Junky Registered User Join Date: Nov 2009 Posts: 14	Omg, you're right!! Tnx
Junky is offline

12-07-2009, 08:20 AM	#9
Junky Registered User Join Date: Nov 2009 Posts: 14	Ok, I'm getting really annoying with this, but I want to understand EOF completely. Code: #include <stdio.h> int main() { int c,nl; nl = 0; while ((c = getchar()) != EOF) if (c == '\n') nl++; printf("%d\n",nl); } This is supposed to count lines. But I can't get to the 'printf' part, because, when I enter EOF (which is CTRL C), I get kicked out of the program. Does anyone know why? (When I was testing it, I entered system("pause"), so that's not the problem).
Junky is offline

12-07-2009, 08:33 AM	#11
BEN10 DESTINY Join Date: Jul 2008 Location: in front of my computer Posts: 803	EOF explained C99 defines EOF as a macro "which expands to an integer constant expression, with type int and a negative value, that is returned by several functions to indicate end-of-file". __________________ HOPE YOU UNDERSTAND....... By associating with wise people you will become wise yourself It's fine to celebrate success but it is more important to heed the lessons of failure We've got to put a lot of money into changing behavior PC specifications- 512MB RAM, Windows XP sp3, 2.79 GHz pentium D. IDE- Microsoft Visual Studio 2008 Express Edition
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12-07-2009, 08:45 AM	#12
Junky Registered User Join Date: Nov 2009 Posts: 14	I understand now. I was confused, because CTRL-Z gave me "^Z", but I just have to press enter. Tnx
Junky is offline

07-28-2010, 01:30 AM	#13
dareck Registered User Join Date: Jul 2010 Posts: 3	I'm reading the same book on C programming as well. Though, Ctrl + Z dosen't seem to work for me. I'm using VS 2008 and windows 7 to run the code. I read somewhere that sometimes you'd have to use Ctrl + V first followed by Ctrl + Z. Is that the right way? Seems to have worked. Has anyone else tried it on windows 7?
dareck is offline

07-28-2010, 01:39 AM	#14
dareck Registered User Join Date: Jul 2010 Posts: 3	and I had to press 'Enter' after Ctrl+v AND Ctrl+z
dareck is offline

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