Detecting keyboard press in Ubuntu C++

Question

In Ubuntu, I would like to write a C++ program which quits whenever the key q is pressed. Until this, the program continues running. But rather than just a loop which checks for input on every iteration, I want to call a function which then calls other functions etc. So, I cannot just keep checking for input in a loop because that loop is never revisited. Do I need to write a separate thread for this, which detects keyboard inputs, or is there something build into Ubuntu which I can use?

Answer 1

It depends on which environment is your program running.

If it runs on the desktop, it is a GUI application, and you need some graphical toolkit like Qt or Gtk (to avoid direct X11 programming). You could consider also libsdl

If it runs in a terminal, you'll better use some terminal library like ncurses (or, if you want a line edition, readline). Read also the tty demystified web page. Notice that the console tty may be raw or cooked (in which case, line buffering happens partly in the kernel!).

You may also want some event loop (but Qt gives you one), so read about poll(2).

If you are not familiar with it, also read Advanced Linux Programming.

Answer 2

Just read stdin and check if it's 'q'

#include <iostream>
#include <boost/thread.hpp>
using namespace std;

void workerFun(const bool& stopFlag)
{
   //Do stuff
   if stopFlag
      return; // probably want to have some logic to clean up, save progress etc
}

int main()
{
    bool flag = false;
    //Start the worker in another thread
    boost::thread workerThread(workerFun, std::ref<bool>(flag));

    //Keep checking if the user wants to quit
    do
    {
       cout<<"Enter q to quit"<<endl;
       char input;
       cin>>input;
       flag = input == 'q' || input == 'Q'
    } while (!flag);
    //user want's to quit, wait for the worker to stop
    workerThread.join();

    cout << "Goodbye!"<<endl;
    return 0;
}