Why I don't get the EOF?

Question

This is my code example. I wrote the question in my comment:

main(){
    long cnt; // chars count
    int c;

    /* Why the 'for' cicle doesn't finish when I input the
     * "a^Z" string and press ENTER? At this case '^Z' is
     * CTRL + Z (i.e this is EOF). I expected the second loop
     * will get the EOF (i.e. -1), but it has 26 instead of. Why?
     */
    for(cnt = 0; (c = getchar()) != EOF; ++cnt)
        ;

    printf("Chars count: %ld", cnt);
}

If I put a, ENTER, CTRL + Z, ENTER then I get the expected result: the CTRL + Z breaks the loop.

UPD

When I read info about getchar function then I saw that it uses the line-buffered input. It expects ENTER for pushing the data. I didn't see info that it also can push data when it get the Ctrl - Z. Therefore I expected that the second value will be EOF in my case (and the loop will be broken), i.e. I expectet that my string line will be parsed like the a, EOF, \n sequence.

@BrandonIbbotson the use of the loop is limted to increment `cnt`. — Sourav Ghosh, Dec 08 '16 at 20:06
ctrl-z is a terminal handled thing probably. It may not do anything if there are still characters on the line. — Iluvatar, Dec 08 '16 at 20:08
Because the `Ctrl-Z` must be the first key entry, or the first after a `newline`. — Weather Vane, Dec 08 '16 at 20:10
@BrandonIbbotson because its body is empty. All what I need it does in the head. — Andrey Bushman, Dec 08 '16 at 20:10
Changing loop code to `for(cnt = 0; (c = getchar()) != EOF; ++cnt) { printf("%ld %d\n", cnt, c); fflush(stdout); }` would enhance the understanding of code functionality. — chux - Reinstate Monica, Dec 08 '16 at 20:21
@AnT Hmm... but my program doesn't get the input until I press `Enter`. So, I see the `Ctrl-Z` doesn't push my data. Am I mistaken? — Andrey Bushman, Dec 08 '16 at 20:21
@chux I get this output: `a^Z`, `0 97`, `1 26`. And the loop is not broken. — Andrey Bushman, Dec 08 '16 at 20:24
What happens when you try the input sequence of [this good answer](http://stackoverflow.com/a/41047963/2410359)? `A`, `Crtl Z`, `Enter`, `Crtl Z`? — chux - Reinstate Monica, Dec 08 '16 at 20:38
What is unclear about the title question "Why I don't get the EOF?" is you do get EOF when you type "a, ENTER, CTRL + Z, ENTER". When you type "a ^Z ENTER", that does not include the correct terminal's EOF sequence indication. C does not define the sequence. It is platform dependent. — chux - Reinstate Monica, Dec 08 '16 at 20:47

score 1 · Accepted Answer · answered Dec 08 '16 at 20:08

1

When you press a+ CTRL + Z and then press ENTER, the CTRL + Z flushes the input (stdin) and the next input is \n, which is not an EOF. You need to press CTRL + Z twice to simulate the second EOF.

answered Dec 08 '16 at 20:08

Sourav Ghosh

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I still don't understand... The `\n` value is `10`, but I get the `26`. – Andrey Bushman Dec 08 '16 at 20:17
1

@AndreyBushman how do you check? – Sourav Ghosh Dec 08 '16 at 20:19
I look the values in the *Watch* window in MS Visual Studio. – Andrey Bushman Dec 08 '16 at 21:02
When I read info about `getchar` function then I saw that it uses the *line-buffered input*. It expects `ENTER` for pushing the data. I didn't see info that it also can push data when it get the `Ctrl - Z`. Therefore I expected that the second value will be `EOF`. – Andrey Bushman Dec 08 '16 at 21:11
I added the *UPD* section in my question. – Andrey Bushman Dec 08 '16 at 21:16

Why I don't get the EOF?

1 Answers1