iOS uuid的生成

+ (NSString *)uuid{
    // create a new UUID which you own
    CFUUIDRef uuidref = CFUUIDCreate(kCFAllocatorDefault);
    // create a new CFStringRef (toll-free bridged to NSString)
    // that you own
    CFStringRef uuid = CFUUIDCreateString(kCFAllocatorDefault, uuidref); 
    NSString *result = (__bridge NSString *)uuid;
    //release the uuidref
    CFRelease(uuidref);
    // release the UUID
    CFRelease(uuid);
    return result;
}