且构网

分享程序员开发的那些事...
且构网 - 分享程序员编程开发的那些事

我应该在C ++中什么时候使用typedef?

更新时间:2022-11-23 11:52:36

模板元编程



许多模板元编程中的

typedef 是必需的

任务 - 每当一个类被视为编译时类型函数时,将使用 typedef 作为编译时类型值生成的类型。例如。考虑一个简单的元函数,用于将指针类型转换为其基本类型:
  template< typename T& 
struct strip_pointer_from;

template< typename T>
struct strip_pointer_from< T *> {//指针类型的部分专门化
typedef T type;
};

示例: strip_pointer_from< double *> :: type 计算为 double 。注意,模板元编程在库开发之外不常用。



简化函数指针类型



typedef 是一种有用的,可以为复杂的函数指针类型提供一个简短的别名:

  typedef int(* my_callback_function_type)(int,double,std :: string); bb 
$ b

In my years of C++ (MFC) programming in I never felt the need to use typedef, so I don't really know what is it used for. Where should I use it? Are there any real situations where the use of typedef is preferred? Or is this really more a C-specific keyword?

Template Metaprogramming

typedef is necessary for many template metaprogramming tasks -- whenever a class is treated as a "compile-time type function", a typedef is used as a "compile-time type value" to obtain the resulting type. E.g. consider a simple metafunction for converting a pointer type to its base type:

template<typename T>
struct strip_pointer_from;

template<typename T>
struct strip_pointer_from<T*> {   // Partial specialisation for pointer types
    typedef T type;
};

Example: the type expression strip_pointer_from<double*>::type evaluates to double. Note that template metaprogramming is not commonly used outside of library development.

Simplifying Function Pointer Types

typedef is helpful for giving a short, sharp alias to complicated function pointer types:

typedef int (*my_callback_function_type)(int, double, std::string);

void RegisterCallback(my_callback_function_type fn) {
    ...
}