CFUUIDRef cfuuid = CFUUIDCreate(kCFAllocatorDefault); NSString *cfuuidString = (NSString*)CFBridgingRelease(CFUUIDCreateString(kCFAllocatorDefault, cfuuid));
生成唯一的随机字符串
原文：http://www.cnblogs.com/shenhongbang/p/5545270.html
