getchar() not returning any output

Question

I was going through some basic C codes and then I found a program intended to count numbers from a given input:

#include <stdio.h>

// count characters given as input

int main()
{
    double nc;

    for(nc = 0; getchar() != EOF; ++nc)
        ;

    printf("%.0f\n", nc);
}

But as I ran the program on terminal (I'm using Debian 11), I'm getting no output for whatever I give as input. But pressing Ctrl+C is terminating the program as it should.

well... in that case you need another book or ... double check how the program is executed — Support Ukraine, Jan 04 '22 at 13:32
Explanation: `getchar` normally never returns EOF because stdin never reach end-of-file. But using CTRL-d you can fake an EOF (for windows that would be CTRL-z as far as I recall) — Support Ukraine, Jan 04 '22 at 13:35
@4386427 pressing ```a``` ```b``` and then immediately Ctrl + D returned nothing. But pressing Enter first and then Ctrl+D returned value 3 that's actually +1 then actual result... And BTW, the book is by Dennis Ritchie :) — Kingshuk Chakravorty, Jan 04 '22 at 13:37
`3` because you have input `3` characters - `a`, `b` and `\n` (new line character due to `ENTER` pressed). — H.S., Jan 04 '22 at 13:38
oh yes... input buffering... that's why you need the ENTER after `a` and `b`. And it prints 3 because it had 3 characters, i.e. `a` `b` and ENTER. So all is good... :-) — Support Ukraine, Jan 04 '22 at 13:39
@H.S. I see... Even a blank input is giving ```1``` as output. But Dennis clearly stated in the book that it should return ```0``` as there isn't actually any output... — Kingshuk Chakravorty, Jan 04 '22 at 13:40
The program **will** return zero! But that has nothing to do with the print outs. After running the program try: `echo $?` — Support Ukraine, Jan 04 '22 at 13:41
Kingshuk Chakravorty, if the count is not expected, change code to `int ch; for(nc = 0; (ch = getchar()) != EOF; ++nc) { printf("%f %d\n", nc, ch); }` to see what is really happening. — chux - Reinstate Monica, Jan 04 '22 at 13:42
Monica I tried your suggestion and gave ```Debian``` as input. It returned two outputs: ```-1``` ```7``` for ```ch``` ```nc``` respectively. — Kingshuk Chakravorty, Jan 04 '22 at 13:47
@KingshukChakravorty Review [comment](https://stackoverflow.com/questions/70579542/getchar-not-returning-any-output#comment124766033_70579542) - Had to edit it Be sure the `printf()` is within the loop, not after. — chux - Reinstate Monica, Jan 04 '22 at 13:49
@KingshukChakravorty, Did you give `"Debian"` as input or `"Debian\n"` as input? (Did you type the _Enter_ key also?) — chux - Reinstate Monica, Jan 04 '22 at 13:52
@chux-ReinstateMonica well... Your suggestion resulted in this: for input ```debian``` (with ENTER key) I got some gibberish output: ```100 0``` ```101 1``` ```98 2``` ```105 3``` ```97 4``` ```110 5``` ```10 6``` all in individual lines for ```ch``` and ```nc``` respectively. — Kingshuk Chakravorty, Jan 04 '22 at 13:53
@KingshukChakravorty 100 is [ASCII](https://en.wikipedia.org/wiki/ASCII) for `d`, 101 is ASCII for `e`, ... 110 is ASCII for `n` and 10 is ASCII for `\n`, the Entry key. 7 characters in all. It that unexpected? — chux - Reinstate Monica, Jan 04 '22 at 13:55
Seems you switched something. chux code will not give that result — Support Ukraine, Jan 04 '22 at 13:56
@chux-ReinstateMonica I got it. So 100, 101... all are ASCII codes for my characters. Thanks for that! :) — Kingshuk Chakravorty, Jan 04 '22 at 14:00
@KingshukChakravorty So was the final output of `printf("%.0f\n", nc);` a `7` (with a new-line) as expected? Any other questions? — chux - Reinstate Monica, Jan 04 '22 at 14:01
@chux-ReinstateMonica No problem at all right now. Thanks for your clarification :D — Kingshuk Chakravorty, Jan 04 '22 at 14:03

score 0 · Answer 1 · answered Jan 04 '22 at 14:09

0

I had to modify you code a little bit to make it work

#include <stdio.h>

#include <signal.h>

static volatile int keepRunning = 1;

void intHandler(int dummy) {
    keepRunning = 0;
}

// count characters given as input

int main()
{
   int nc = -1;
   signal(SIGINT, intHandler);
   while (keepRunning) { 
       nc = 0;
       for(nc = 0; getchar() != EOF; ++nc)
           ;
    }
    if(nc != -1)
      printf("%i", nc);
}

pressing ctrl + c will terminate the program before printing nc, so we have to catch the user pressing CTRL+C, sing signal library
see this: Catch Ctrl-C in C

answered Jan 04 '22 at 14:09

ahmed deeb

19
5

remember that new line is actually a character too, '\n' – ahmed deeb Jan 04 '22 at 14:10
no output this time :) – Kingshuk Chakravorty Jan 04 '22 at 14:15
start the program on terminal and write what ever you want then press ctrl+c, it should work – ahmed deeb Jan 04 '22 at 14:16
Nope... Ctrl+C now not even terminating the program. Just printing a bunch of ```^C``` on window. – Kingshuk Chakravorty Jan 04 '22 at 14:18
with this approach the `for` loop shall be removed – Support Ukraine Jan 04 '22 at 14:20

score 0 · Answer 2 · answered Jan 04 '22 at 14:24

0

I am using Win10, MS compiler, it worked fine...

C:\Users\Ahmed\Desktop>cl test.c
Microsoft (R) C/C++ Optimizing Compiler Version 17.00.50727.1 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

test.c
Microsoft (R) Incremental Linker Version 11.00.50727.1
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test.exe
test.obj

C:\Users\Ahmed\Desktop>test.exe
adkjlad
asldkjasd
18
C:\Users\Ahmed\Desktop>

answered Jan 04 '22 at 14:24

ahmed deeb

19
5

But on Debian it's not working... – Kingshuk Chakravorty Jan 04 '22 at 14:31

getchar() not returning any output

2 Answers2