How to execute commands WHILE taking input?

Question

How can i execute some commands while waiting for an input?

Something like this:

while(/*taking input*/) {
    sleep(15);
    cout<<"You still there?";

    //...     
}

So it asks for the input, but while it waits for ENTER to be pressed it executes commands.
Is it possible?

Edit:
Thanks for all the suggestions :)

multithreading. Although if you print something to console WHILE user is typing, things can get messy/confusing for the user. — SigTerm
– SigTerm, Commented Sep 17, 2013 at 15:09
As I said, I'm still a newbie. Thanks anyways, I'll figure it out :) — Immortal Fire
– Immortal Fire, Commented Sep 17, 2013 at 15:10
Multithreading is way too big a cannon for this tiny problem. A simple non-blocking I/O multiplexing loop should do just fine. — Kerrek SB
– Kerrek SB, Commented Sep 17, 2013 at 15:16
That was just an example. I want to use it for a chat, so while the 1st thread is used to send messages, the 2nd is used to receive messages :) — Immortal Fire
– Immortal Fire, Commented Sep 17, 2013 at 15:18

Bartek Banachewicz · Accepted Answer · 2013-09-18 09:48:46Z

3

Using C++11 threading facilities, you can simply spawn a "worker" thread that does the work while you wait for the input.

std::async is an easy way to asynchronously get a result of an operation; your problem description isn't very precise, so I don't know what else I might add here.

It can be done without threading, but then you would need an asynchrounous access to the input, which in general isn't cross-platform.

After Martin's comment, I actually see the problem with a greater clarity; in this case, your best bet is probably to look for more abstracted IO APIs, which will provide nonblocking input, or create your own based on OS-specific API.

edited Sep 18, 2013 at 9:48

answered Sep 17, 2013 at 15:28

Bartek Banachewicz

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1 Comment

R. Martinho Fernandes Over a year ago

No, threads don't help for this kind of work. I/O is blocking and serialised. Spawning threads won't help output stuff while waiting for input. C++ simply does not provide for this at all.

Hulk · Accepted Answer · 2013-09-17 15:35:01Z

2

There are 2 ways to achieve your objective:

Multithreading
Asynchronous IO

For the use case you mentioned (a chat), I'd recommend to look into the second option. You may want to have a look at the documentation for boost asio, which contains an example for a chat client and server.

answered Sep 17, 2013 at 15:35

Hulk

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Paul Evans · Accepted Answer · 2013-09-17 15:35:44Z

1

You want to spawn another thread to run in parallel with the thread's that's waiting for i/o (input from stdin in this case). Run whatever it is you want to do while waiting for i/o in that spawned thread. Have a look at Boost threads

edited Sep 17, 2013 at 15:35

answered Sep 17, 2013 at 15:27

Paul Evans

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BigTailWolf · Accepted Answer · 2013-09-17 15:52:58Z

0

If you allow to add something outside your segment, it will work:

[wolf@Targaryen]:~$ cat main.cpp 
#include <iostream>
#include <string>
using namespace std;

int main() {
  string s;
  while( getline(cin, s) and s != "" ) {
    cout << "You still there?" << endl;
  }
}
[wolf@Targaryen]:~$ r
adb
You still there?
sfcetgw
You still there?
wefew
You still there?

[wolf@Targaryen]:~$

answered Sep 17, 2013 at 15:52

BigTailWolf

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