iphone生成唯一字符串

在iphone里写文件，需要生成唯一的文件名。

一种方法事采用UUID

+ (NSString *)GetUUID
{
  CFUUIDRef theUUID = CFUUIDCreate(NULL);
  CFStringRef string = CFUUIDCreateString(NULL, theUUID);
  CFRelease(theUUID);
  return [(NSString *)string autorelease];
}

来源 http://stackoverflow.com/questions/427180/how-to-create-a-guid-uuid-using-the-iphone-sdk

另一种方法用具体的时间生成文件名

[[NSCalendarDate calendarDate] descriptionWithCalendarFormat:@"%m%d%Y%H%M%S%F"]

http://developer.apple.com/iphone/library/documentation/cocoa/Conceptual/DatesAndTimes/Articles/LegacyNSCalendarDate.html

来源：http://stackoverflow.com/questions/3298022/generate-unique-temporary-file-paths