// new callbacks based on C++11
#define CC_CALLBACK_0(selector,target, …) std::bind(&selector,target, ##VA_ARGS)
#define CC_CALLBACK_1(selector,target, …) std::bind(&selector,target, std::placeholders::_1, ##VA_ARGS)
#define CC_CALLBACK_2(selector,target, …) std::bind(&selector,target, std::placeholders::_1, std::placeholders::_2, ##VA_ARGS)
#define CC_CALLBACK_3(selector,target, …) std::bind(&selector,target, std::placeholders::_1, std::placeholders::_2, std::placeholders::_3, ##VA_ARGS)
… 和##VA_ARGS 是什么意思?