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