Resetting stdin after EOF

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

Code:

---

#include <stdio.h>

int main()
{
    int c;
    while ((c = getchar()) != EOF ) {
        putchar(c);
    }
    printf( "EOF from file, now reading stdin\n" );
    clearerr(stdin);
    while ((c = getchar()) != EOF ) {
        putchar(c);
    }
    printf( "All done\n" );
    return 0;
}

---

Points to note
1. c is declared as int - which you need if you're ever going to separate the value of EOF from any character.
2. main returns a value.

Now the clearerr(stdin); is only going to work if your input starts off with the keyboard (you can press ctrl-D twice, and it will execute both loops).
However, redirected input ( via < or | ) isn't going to work like that, once EOF is detected, that's it.

So in order to process some input, then process stdin, you need to do something like this

Code:

---

cat hello.c - | ./a.out
( dmesg ; cat - ) | ./a.out

---

Use "cat -" to read from stdin and copy it to the pipe to your program.

But what if I can't do that? I need the user to be able to simply redirect input to the program, rather than to have them execute a complicated expression in doing so.
Take the program "less" as an example - it can get redirected input, and then perfectly happily accept keyboard input from the user, so there must be some way of doing it :confused:

Is there any way I could reset the terminal and so set stdin to keyboard input again, as it were?

Well I suggest you read the source code to less then.

But the answer is almost certainly far from portable, since it's likely to read from the terminal directly rather than from stdin.

There is a way, but like Salem said, it's definitely not portable. This works on my Linux box though:

Code:

---

itsme@itsme:~/C$ cat filethenstdin.c
#include <stdio.h>

int main(void)
{
  char buf[BUFSIZ];

  puts("Reading from stdin...");
  while(fgets(buf, sizeof(buf), stdin))
    fputs(buf, stdout);

  freopen("/dev/tty", "rw", stdin);

  puts("Reading from stdin again...");
  while(fgets(buf, sizeof(buf), stdin))
    fputs(buf, stdout);

  return 0;
}

---

Code:

---

itsme@itsme:~/C$ cat search.txt
a
b
c
d
e
f
g
itsme@itsme:~/C$ ./filethenstdin < search.txt
Reading from stdin...
a
b
c
d
e
f
g
Reading from stdin again...
this is a test
this is a test
yay
yay
^d
itsme@itsme:~/C$

---

It works because /dev/tty always points to the user's terminal.