Re: Take in a command while doing something else

Stuart Golodetz <>
Mon, 12 Oct 2009 16:20:32 +0100
Sam wrote:

Stuart Golodetz writes:

Sam wrote:

Nick W writes:

Hi all,

I will be using a C++ program to control a robot, and would like to
"accept" keyboard-entered commands (strings) while the program is
running and controlling the robot as a part of the control cycle. What
is the best way of doing this please?

The C++ programming language does not define any entity which is
called a "keyboard". Your question is about the specific C++
implementation you are using, rather than the C++ language itself,
and the correct answer to your question depends on your specific C++
implementation and operating system. The answer would be different,
for example, was your application running on Microsoft Windows,
Linux, or Mac.

You can do platform-independent input by just reading from std::cin

Read OP's original message and pay attention. He is asking for reading
cin only when input is available. poll() or select() is not available

Actually he didn't say that - although I agree it's probably what he'll
ultimately want. I did pay attention to what he did say, which was that
he wanted to accept commands entered at the keyboard and use them to
control the robot. As a very hacked-together example:

#include <iostream>
#include <string>

#include <boost/thread/thread.hpp>

boost::mutex doneMutex;
bool done = false;

void robot_controller()
        boost::mutex::scoped_lock lock(doneMutex);
        if(done) break;

        // TODO: Do something interesting here

void user_input()
        std::cout << "Enter a command: ";

        std::string cmd;
        std::getline(std::cin, cmd);

        if(cmd == "quit")
            boost::mutex::scoped_lock lock(doneMutex);
            done = true;

int main()
    boost::thread rcThread(robot_controller);
    boost::thread uiThread(user_input);
    return 0;

Best wishes,

The fact that the specification for the C++ language (note: not the
language itself) doesn't define what a "keyboard" is doesn't mean that
you can't portably get some sort of input from a keyboard (you might not

Yeah, but that was not the original question.

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