How to tap/hook keyboard events in OSX and record which keyboard fires each event

Question

I\'ve now discovered how to hook/tap keyboard events on OS X at a low level: How to tap (hook) F7 through F12 and Power/Eject on a MacBook keyboard

Printing out the

Answer 1

I was working on this problem, and finally got the solution. OP's code is correct, if you'd like the product ID of the keyboard/pad, add lines to the myHIDKeyboardCallback() function:

void myHIDKeyboardCallback(void* context,  IOReturn result,  void* sender,  IOHIDValueRef value){

    IOHIDElementRef elem = IOHIDValueGetElement(value);
    if (IOHIDElementGetUsagePage(elem) != 0x07)
        return;

    IOHIDDeviceRef device = sender;
    int32_t pid = 1;
    CFNumberGetValue(IOHIDDeviceGetProperty(device, CFSTR("idProduct")), kCFNumberSInt32Type, &pid);

    uint32_t scancode = IOHIDElementGetUsage(elem);

    if (scancode < 4 || scancode > 231)
        return;

    long pressed = IOHIDValueGetIntegerValue(value);

    printf("scancode: %d, pressed: %ld, keyboardId=%d\n", scancode, pressed, pid);
}

As @pmdj said you can use IOHIDDeviceRegisterInputValueCallback(), I was having trouble with this, and found that sender argument provided keyboard product id anyways.