Weird behaviour of getchar regarding EOF

Question

I'm writing a program that gets characters from the user using getchar and counts them. It's supposed to stop when the user enters EOF, print out the char count and print done. The code:

char cur = 0;
int count = 0;
while((cur = getchar()) != EOF){
    ++count;
}
printf("\n%d", count);
printf("\ndone\n");

However the loop doesn't stop until the user enters 2 consecutive EOF. I tried to force the loop to stop by by manually checking if the char is EOF and breaking the loop but it doesn't seem to work.

How can I make it stop after just one EOF?

How does a user "enter" `EOF`? It is not a key but a condition that is signaled in some fashion. What keys did you press? — chux - Reinstate Monica, Apr 18 '17 at 19:18
The `EOF` key typed (`Ctrl-D` on Linux, `Ctrl-Z` on Windows) must be the first character after a `newline`. Even then, I have not figured out why it sometimes needs more than one `EOF` from the keyboard. — Weather Vane, Apr 18 '17 at 19:20
@MichaelSapozhnikov I wonder then how `(char)4` (a "control D") as keyboard input is entered? — chux - Reinstate Monica, Apr 18 '17 at 19:23
`getchar` returns an `int`, not a `char` and either `EOF` or the full character codes cannot fit into a `char` (depends on its signed-ness). — too honest for this site, Apr 18 '17 at 19:48

dbush · Accepted Answer · 2017-04-18T19:32:31.933

2

The getchar function is declared to return an int, not a char. Because you're assigning the result to a char, you won't be able to capture an EOF.

Change the datatype of cur to int.

EDIT:

This most likely has to do with how your terminal handles EOF. When I tested this, if I enter one or more characters on a line and then press CTRL-D, the characters (minus the CTRL-D) are sent to the program and read by getchar. If I press CTRL-D on a line by itself, even if I pressed ENTER to input the prior line, then EOF is detected.

If you were to redirect a file into the stdin of this program, you'd see that EOF is detected when the end of the file is reached.

edited Apr 18 '17 at 19:32

answered Apr 18 '17 at 19:16

dbush

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So if the first EOF cannot be recognised from a char, then why is the second? – Yunnosch Apr 18 '17 at 19:18
Thank you, woked like magic, but the question still interests me why does the 2nd time work but not the first? – Michael Sapozhnikov Apr 18 '17 at 19:23

Weird behaviour of getchar regarding EOF

1 Answers1