A small test program for reading events from a joystick/gamepad on Linux using Apple's libdispatch to handle io operations asynchronously.

dispatch_joystick.cpp

#include <iostream>
#include <cstring>
#include <cerrno>
#include <unistd.h>

#include <linux/joystick.h>
#include <linux/input.h>
#include <sys/ioctl.h>

#include <dispatch/dispatch.h>

using namespace std;

int main (int argc, char** argv)
{
    // Open the joystick
    int fd = open("/dev/input/js0", O_RDONLY);
    if(fd < 0)
    {
        cerr << "Unable to open joystick" << endl;
        return 1;
    }

    // Get joystick info
    int axis_count = 0, button_count = 0;
    char name[128];
    ioctl(fd, JSIOCGAXES, &axis_count);                /* Get the number of axes in the joystick */
    ioctl(fd, JSIOCGBUTTONS, &button_count);           /* Get the number of buttons in the joystick */
    ioctl(fd, JSIOCGNAME(80), (char *) name);          /* Get the name of the joystick */

    // Print joystick information
    cout << "----- " << name << " ------" << endl;
    cout << " Axis Count: " << axis_count << endl;
    cout << " Button Count: " << button_count << endl;
    cout << "---------------------------" << endl;

    // Locate the high priority queue
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0);

    // Create a libdispatch io channel for the joystick
    dispatch_io_t joystickChannel = dispatch_io_create(DISPATCH_IO_STREAM, fd, queue, ^(int error)
    {
        if(error)
        {
            cerr << "Got an error from Joystick: " << error << " (" << strerror(error) << ")" << endl;
        }
    });

    // Don't bug user unless we've received at least a js_Event object
    dispatch_io_set_low_water(joystickChannel, sizeof(struct js_event));
    dispatch_io_set_high_water(joystickChannel, sizeof(struct js_event));

    // Establish a read handler
    dispatch_io_read(joystickChannel, 0, SIZE_MAX, queue, ^(bool done, dispatch_data_t data, int error)
    {
        // Did we successfully get data?
        if(data)
        {
            // Apply an operation to the received data
            dispatch_data_apply(data, ^(dispatch_data_t, size_t, const void *location, size_t size)
            {
                const struct js_event *event = static_cast<const struct js_event *>(location);
                switch (event->type & ~JS_EVENT_INIT)
                {
                    case JS_EVENT_AXIS:
                    cout << "Axis " << (int) event->number << ": " << (int) event->value << endl;
                    break;

                    case JS_EVENT_BUTTON:
                    cout << "Button " << (int) event->number << ": " << (int) event->value << endl;
                    break;
                }

                // Success
                return true;
            });
        }
    });

    dispatch_main();

    return 0;
}