Thread: reading from stdin

hello

I can't figure out how to make a program which won't get paused reading from the stdin.
Here is an example:

Code:

string input_line;

while (true) {

   if ("stdin is not empty") {
      cin >> input_line;
   }

   ... (some code to execute continuously)
}

I'm going to execute the program under linux so:

Code:

$ tail -f file.txt | ./program

thanks in advance for help

Hi Prelude

I've looked about kbhit()
That function (wich seems being working only under borland-family compilers) concerns the key management, that is not what I'm searching for.
A web research sends me around keyboard-input related functions, which I already know.

My program needs to do his own stuff until it will check that the stdin is not empty.

Thanks for the answer anyway

edit: I don't need it to be portable, at the moment, I'm working under linux

ok

Imagine a server software that manages, say, a chat network,
running in background.
If I want to send some messages to the server (like restart or shutdown, etc.)
I should do that through a temporary file, which the program will read everytime I add a new line to it.

Using for example "cin.get ()" will pause the server, until I send it a new message.

So I'd need something like "cin.empty ()" to check if the server is receiving any message from the stdin or not.

Hope it is clearer now.

What about cin.peek()? I'm not sure if peek() blocks or just returns EOF if nothing is in the buffer?

in_avail should work, as c++ reference says:
http://www.cplusplus.com/reference/i.../in_avail.html

but my test program didn't work...
any suggestion about?

edit: looking for peek ()

Code:

// test.cpp
int main ()
{
	string line;

	cout << "Input: ";
	cin >> line;

	cout << "in_avail: " << cin.rdbuf ()->in_avail () << endl;

	return 0;
}

shell output:

Code:

$ g++ -o test test.cpp
$ ./test
Input: hello
in_avail: 0

On linux you could use select().
You probably have to set stdin to unbuffered mode.

checked out: peek () blocks the program.

You probably have to set stdin to unbuffered mode.

what does it mean?

Originally Posted by King Mir

It says that in_avail calls showmanyc(). That function can check if underflow is possible, and return the number of available characters. However there is no requirement that cin implements this functionality; the default behavior is simply to return 0.

Ok thanks, I don't know what "underflow" means exactly, but I figured out what the matter is.

-----------------------------
select() seems to be the right way, checking it out...

Originally Posted by carlorfeo

what does [unbuffered] mean?

matsp and other linux people can explain that. I haven't worked on unix for quite a few years. And I'm just guessing that stdin would have to be unbuffered for what you want. That may not be the case.