How to Determine if STDIN is Empty?

Question

I'm writing an emulator for my Operating Systems course. The problem I have is that we need to get all our .job files (they are like application programs being fed to the emulator) from STDIN and read them in.

Call:

./RMMIX < aJob.job

I just slurp it with

while(getline(std::cin, line)) 

line by line. The problem is, if I do not put anything to STDIN, then cin will wait for user input- NOT what I want. I need the program to recognize a lack of text on STDIN and terminate, not wait for user input instead.

I have determined that I can query the length like so:

size_t beg = std::cin.tellg();
std::cin.seekg(0, std::ios_base::end);
size_t end = std::cin.tellg();
std::cin.seekg(0, std::ios_base::beg);

and terminate if std::cin has a length of 0.

Are there any other solutions to this? Is this a portable solution?

Answer 1

I don't think there's a platform independent way of doing this, but on Unix-based systems you should be able to do:

#include <unistd.h>
...

int main() {
    if (!isatty(0)) {
        // stdin is being streamed from a file or something else that's not a TTY.
    }

    ...
}

However, I think doing it via a command line option is the preferred approach.