Question

The following code simply echoes the standard input to the standard output. If I run the program like so ./a.out, I can type anything and the program works fine. However, if I run it like this ./a.out < input.txt I get an infinite loop, regardless of the content of input.txt.

#include <iostream>

using namespace std;

int main() {
  string input;
  while (true) {
    cout << "Type your input: ";
    getline(cin, input);
    cout << input << endl;
  }
  return 0;
}

What am I doing wrong?

EDIT: To clarify, I expect that after the input from the input file is finished, getline waits for more input from stdin. Instead, it continues to read when nothing is there.

Answer 1

You don’t have a terminating condition for your loop: while (true) is an infinite loop in any case – that is, without a break/exit/etc. in the loop body.

I’m guessing that when using your program to echo stdin you end it by pressing Ctrl-C. Run your program using ./a.out, and type Ctrl-D (EOF): you’ll also get an infinite loop.

Look over the docs for getline: use the return value to end your loop:

while (getline(cin, input))