Resetting stdin after EOF (C)

I have a piece of code that looks like this:

---example.c---

Code:

---

#include <stdio.h>

int main() {
        char c;
        while ((c = getchar()) && (c != EOF))
                ;
        putchar('\n');
        c = getchar();
        printf("%c\n", c);
}

---

Entering input from the keyboard, this program works fine.
However, if I then redirect input to this program (e.g. dmesg | ./example), then I get a garbage character printed to the console, and the program does not wait for input from the keyboard.
I assume this is something to do with resetting stdin - how can I pass input back to the keyboard?

Thanks,
Rob

Um.... getchar() returns an int, not a char. ;) Your loop will terminate early if your input ever has a byte with value 255 in it (EOF, or -1, cast to a char, has value 255).

You need to declare c as an int, and check it against EOF as an int. Only after you've determined that it isn't EOF, is it safe to cast it to a char.

Quote:

---

However, if I then redirect input to this program (e.g. dmesg | ./example), then <...> the program does not wait for input from the keyboard.

---

That's exactly how it's supposed to work ;)

When input is coming from another command instead of the keyboard, your program can't wait for the user to press a key when your program is finished. It has no way of talking to the keyboard.

I also believe that reading characters after you've hit EOF is explicitly undefined (i.e., anything can happen and it'll still be a legal C implementation), though I might be wrong on that. If you were reading from a normal file, you'd be able to fseek backwards to "reset" the file handle, but stdin is un-seekable, so that won't work either.

So I'm not sure what you were trying to accomplish here, but there's probably a better way to do it.

Unfortunately not - the program I gave was just a simple example to illustrate the problem, rather than what I actually needed.
I found a solution, though it isn't portable:

fclose(stdin);
inp = fopen(CURRENT_TTY, "r");
c = getc(inp);

does the trick, though it's not too nice. Thanks anyway.