这里加入一个插曲,是关于Cocos2d-x回调函数的。首先,让我们Cocos支持的回调函数宏有哪些,以及其原型:
// 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__)
右上边,以上共4个回调函数宏。都是通过C++11新增加bind()实现的。原型如下:
template <class Fn, class... Args> /* unspecified */ bind (Fn&& fn, Args&&... args); with return type (2) template <class Ret, class Fn, class... Args> /* unspecified */ bind (Fn&& fn, Args&&... args);
使用如下,见http://www.cplusplus.com/reference/functional/bind/?kw=bind。
// bind example #include <iostream> // std::cout #include <functional> // std::bind // a function: (also works with function object: std::divides<double> my_divide;) double my_divide (double x, double y) {return x/y;} struct MyPair { double a,b; double multiply() {return a*b;} }; int main () { using namespace std::placeholders; // adds visibility of _1, _2, _3,... // binding functions: auto fn_five = std::bind (my_divide,10,2); // returns 10/2 std::cout << fn_five() << ‘\n‘; // 5 auto fn_half = std::bind (my_divide,_1,2); // returns x/2 std::cout << fn_half(10) << ‘\n‘; // 5 auto fn_invert = std::bind (my_divide,_2,_1); // returns y/x std::cout << fn_invert(10,2) << ‘\n‘; // 0.2 auto fn_rounding = std::bind<int> (my_divide,_1,_2); // returns int(x/y) std::cout << fn_rounding(10,3) << ‘\n‘; // 3 MyPair ten_two {10,2}; // binding members: auto bound_member_fn = std::bind (&MyPair::multiply,_1); // returns x.multiply() std::cout << bound_member_fn(ten_two) << ‘\n‘; // 20 auto bound_member_data = std::bind (&MyPair::a,ten_two); // returns ten_two.a std::cout << bound_member_data() << ‘\n‘; // 10 return 0; }
关于##__VA_ARGS__见博客地址:http://www.cnblogs.com/zhujudah/archive/2012/03/22/2411240.html
至于__selector__和__target__应该是cocos自定义的东西,我在c99中没有找到对应的东西,有时间得对照下c11的定义(csnd恰巧今天在维护服务器,没下载下来)。
而关于placehoders命名空间内容如下:
namespace placeholders { extern /* unspecified */ _1; extern /* unspecified */ _2; extern /* unspecified */ _3; // ... }
时间: 2024-10-10 02:47:06