Program prints garbage upon EOF

Question

I'm reading through the K&R book and implemented the 'copy' example:

#include <stdio.h>

int main() {
    char c;
    while ((c = getchar()) != EOF) {
        putchar(c);
    }
    return 0;
}

All normal input appears to work correctly but when an EOF (^D) is entered the program prints infinite "�" characters and I must halt the program manually.

I have tried using putchar(c); as well as printf("%c", c); to the same effect.

Does anyone know the cause of this?

It should be `int c;`. Is this really from K&R as is? – Eugene Sh. Jul 12 '19 at 17:56 — Eugene Sh., Jul 12 '19 at 17:56
This is correct and no, I copied it wrong. – Liam Seymour Jul 12 '19 at 18:02 — Liam Seymour, Jul 12 '19 at 18:02

score 0 · Answer 1 · answered Jul 12 '19 at 17:58

0

Using int c instead of char c should solve your issue

answered Jul 12 '19 at 17:58

Nicholas Domenichini

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score 0 · Accepted Answer · answered Jul 12 '19 at 18:00

Since c is of type char, an int value returned from getchar will be converted to the type char before it is compared to EOF.

Since the EOF is an in-band error mechanism, it has to be an error value that can be distinguished from all valid characters that could be returned. When you assign EOF to a char you discard information.

After executing:

char c = EOF;

the statement

c == EOF

is false.

Preserve the return type of getchar by doing:

int c;

instead of:

char c;

Program prints garbage upon EOF

2 Answers2