生成随机guid串的代码

1. + (NSString*) stringWithUUID {
2.    CFUUIDRef    uuidObj = CFUUIDCreate(nil);//create a new UUID
3.    //get the string representation of the UUID
4.    NSString    *uuidString = (NSString*)CFUUIDCreateString(nil, uuidObj);
5.    CFRelease(uuidObj);
6.    return [uuidString autorelease];
7. }