typedef

问题 There are two cases where typedef confuses me when it comes to extern template declaration and explicit template instantiation . To illustrate the two see below 2 example code snippets. Consider following example (Case 1) : // suppose following code in some cpp file template <typename T> struct example { T value; }; // valid typedefs typedef example<int> int_example; typedef example<std::string> string_example; // explicit instantiation using above typedefs template class int_example; // ->

问题 It is very difficult for me to explain this particular problem/question so please bear with me (I am having trouble with all my template related questions!). Take this code as an example (note that the point of showing the code is to show a complex template hierarchy, not whether it makes sense): #include <string> #include <vector> #include <list> template <typename T> struct Foo { typedef typename T::value_type value_type; typedef typename T::value_type1 value_type1; typedef typename T:

问题 I've just started working with C++ after not having worked with it for quite a while. While most of it makes sense, there are some bits that I'm finding a bit confuddling. For example, could somebody please explain what this line does: typedef bool (OptionManager::* OptionHandler)(const ABString& value); 回答1: It defines the type OptionHandler to be a pointer to a member function of the class OptionManager , and where this member function takes a parameter of type const ABString& and returns

问题 I have the following code in my C header file: typedef struct mb32_packet_t { uint8_t compid; uint8_t servid; uint8_t payload[248]; uint8_t checksum; } __attribute__((packed)) mb32_packet_s; Doing the following works: struct mb32_packet_t packet; When using this: mb32_packet_t packet; I get: Type 'mb32_packet_t' could not be resolved Unknown type name 'mb32_packet_t'; use 'struct' keyword to refer to the type Isn't typedef struct intended for exactly this purpose, i.e. to be able to omit the

问题 I have the following code in my C header file: typedef struct mb32_packet_t { uint8_t compid; uint8_t servid; uint8_t payload[248]; uint8_t checksum; } __attribute__((packed)) mb32_packet_s; Doing the following works: struct mb32_packet_t packet; When using this: mb32_packet_t packet; I get: Type 'mb32_packet_t' could not be resolved Unknown type name 'mb32_packet_t'; use 'struct' keyword to refer to the type Isn't typedef struct intended for exactly this purpose, i.e. to be able to omit the

问题 This question already has an answer here : C++ template typedef (1 answer) Closed 6 years ago . How can I solve this error? My header file template<typename T> class C1 { public: typedef std::vector<T::F> TFV; TFV Function1(); }; My CPP file template<typename T> TFV C1::Function() //error: ‘TFV’ does not name a type { } 回答1: First of all, use the typename keyword to tell the compiler to interpret F as the (qualified) name of a type: typedef std::vector<typename T::F> TFV; // ^^^^^^^^ Secondly

问题 This question already has an answer here : C++ template typedef (1 answer) Closed 6 years ago . How can I solve this error? My header file template<typename T> class C1 { public: typedef std::vector<T::F> TFV; TFV Function1(); }; My CPP file template<typename T> TFV C1::Function() //error: ‘TFV’ does not name a type { } 回答1: First of all, use the typename keyword to tell the compiler to interpret F as the (qualified) name of a type: typedef std::vector<typename T::F> TFV; // ^^^^^^^^ Secondly

问题 This question already has an answer here : C++ template typedef (1 answer) Closed 6 years ago . How can I solve this error? My header file template<typename T> class C1 { public: typedef std::vector<T::F> TFV; TFV Function1(); }; My CPP file template<typename T> TFV C1::Function() //error: ‘TFV’ does not name a type { } 回答1: First of all, use the typename keyword to tell the compiler to interpret F as the (qualified) name of a type: typedef std::vector<typename T::F> TFV; // ^^^^^^^^ Secondly

问题 As in stl containers, why can't we access a typedef inside the class from the class instance? Is there a particular insight into this? When value_type was a template parameter it could help making more general code if there wasn't the need to specify the template parameters as in vector::value_type Example: class T { public: typedef int value_type; value_type i; }; T t; T::value_type i; // ok t.value_type i; // won't work 回答1: The answer is use decltype to get the class first. E.g., decltype

问题 I am making a stretchy-buffer-like single-file header library for queues in C. I am passing the array as a void* and the size of a single element to one of the functions: void func(void* arr, size_t itemsize); Inside func() I need to do some pointer arithmetic with arr . I can't do arithmetic with void* , so I thought I could create a data type of size itemsize that I could cast arr into, and thus solve my problem. I saw the accepted this question, but would pointer arithmetic on char*[] work