Joystick Test Code for Linux

joy_tester.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/joystick.h>

/*
 * Compiles on linux systems only!
 *
 * Compile it with:
 *
 *     gcc joy_tester.c -o joy_tester
 *
 * This program infinitely reads joystick events from /dev/input/jsN
 * and outputs them to STDOUT. 
 */
int main(int argc, char** argv) {
    struct js_event msg;
    char* joystick;
    char* event_type = "none";
    
    // joystick metadata
    char joystick_name[1024] = "unknown";
    unsigned char num_buttons = 0;
    unsigned char num_axes = 0;
    
    // Choose a device file to read, or default to /dev/input/js0
    if (argc < 2) {
        joystick = "/dev/input/js0";
    } else {
        joystick = argv[1];
    }
    
    // Open the device file for reading
    int fd = open(joystick, O_RDONLY);

    // Get the name of the joystick
    ioctl(fd, JSIOCGNAME(sizeof joystick_name), joystick_name);
    
    // Get the number of axes on the joystick
    ioctl(fd, JSIOCGAXES, &num_axes);

    // Get the number of buttons on the joystick
    ioctl(fd, JSIOCGBUTTONS, &num_buttons);

    // Infinitely read joystick events from the device file
    while (1) {
        if (read(fd, &msg, sizeof(struct js_event)) != sizeof(struct js_event)) {
            printf("Could not read from joystick.\n");
            exit(1);    
        } else {
            if (msg.type == JS_EVENT_BUTTON) {
                event_type = "button";
            } else if (msg.type == JS_EVENT_AXIS) {
                event_type = "axis";
            } else if (msg.type == JS_EVENT_INIT) {
                event_type = "initialization";
            }
            
            printf("Action Performed!\n"
                   "  joystick name: %s\n"
                   "  number of buttons: %u\n"
                   "  number of axes: %u\n"
                   "  value: %d\n"
                   "  event type: %s\n"
                   "  axis/button number: %u\n"
                   "  timestamp: %u\n"
                   "===\n"
                   , joystick_name
                   , num_buttons
                   , num_axes
                   , msg.value
                   , event_type
                   , msg.number
                   , msg.time);

            usleep(10000);
        }
    }

    return 0;
}