Question about EOF.

This is a discussion on Question about EOF. within the C Programming forums, part of the General Programming Boards category; I was reading a book about C programming, and I came across this program example: Code: #include <stdio.h> int main() ...

  1. #1
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    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?

  2. #2
    ATH0 quzah's Avatar
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    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.
    Hope is the first step on the road to disappointment.

  3. #3
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    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 11:52 AM.

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    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')?

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    Quote Originally Posted by Junky View Post
    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.

    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.

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    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 04:42 AM.

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    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).

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    Omg, you're right!!
    Tnx

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    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).

  10. #10
    DESTINY BEN10's Avatar
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    Quote Originally Posted by Junky View Post
    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).
    HOPE YOU UNDERSTAND.......

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  11. #11
    DESTINY BEN10's Avatar
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    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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    I understand now. I was confused, because CTRL-Z gave me "^Z", but I just have to press enter. Tnx

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    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?

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

  15. #15
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    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.
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