c++11模板:获取函数的参数类型

灰太狼 2022-03-17 08:53 375阅读 0赞

假设我们已经知道一个函数类型的定义`double(unsigned char*, unsigned char*)`,如何获取这个函数定义中的输入和输出参数类型呢？  
c++11提供的模板函数`std::function`和`std::tuple_element`可以将一个函数定义的输入和输出参数类型一个一个解析出来，下面是实现代码

#include <functional>
    #include <tuple>
    
    #include <windows.h>
    #include "FSFaceSDK.h"
    template<typename T> 
    struct function_traits;  
    // R为返回类型
    // ...Args 为输入参数类型，个数不限
    template<typename R, typename ...Args> 
    struct function_traits<std::function<R(Args...)>>
    {
        
        static const size_t nargs = sizeof...(Args);
    	// 返回类型
        typedef R result_type;
    
    	// 输入参数类型,i为从0开始的参数类型索引
        template <size_t i>
        struct arg
        {
        
            typedef typename std::tuple_element<i, std::tuple<Args...>>::type type;
        };
    };
    inline double compare(const face_code &f1,const face_code&f2){
        
    
    	typedef std::function<double(unsigned char*, unsigned char*)> feacomp_fun;
    	return (double)FSCompare(
    		/* 强制类型转换为function_traits<feacomp_fun>::arg<0>::type,第一个输入参数类型 */
    		(function_traits<feacomp_fun>::arg<0>::type)f1.element,	
    		/* 强制类型转换为function_traits<feacomp_fun>::arg<1>::type,第一个输入参数类型 */
    		(function_traits<feacomp_fun>::arg<1>::type)f2.element);
    }

参考资料  
[https://stackoverflow.com/questions/9065081/how-do-i-get-the-argument-types-of-a-function-pointer-in-a-variadic-template-cla][https_stackoverflow.com_questions_9065081_how-do-i-get-the-argument-types-of-a-function-pointer-in-a-variadic-template-cla]  
[https://en.cppreference.com/w/cpp/utility/functional/function][https_en.cppreference.com_w_cpp_utility_functional_function]  
[https://en.cppreference.com/w/cpp/utility/tuple/tuple\_element][https_en.cppreference.com_w_cpp_utility_tuple_tuple_element]

[https_stackoverflow.com_questions_9065081_how-do-i-get-the-argument-types-of-a-function-pointer-in-a-variadic-template-cla]: https://stackoverflow.com/questions/9065081/how-do-i-get-the-argument-types-of-a-function-pointer-in-a-variadic-template-cla
[https_en.cppreference.com_w_cpp_utility_functional_function]: https://en.cppreference.com/w/cpp/utility/functional/function
[https_en.cppreference.com_w_cpp_utility_tuple_tuple_element]: https://en.cppreference.com/w/cpp/utility/tuple/tuple_element