forward-declaration

来源： https://stackoverflow.com/questions/35150772/friend-function-template-with-default-template-argument

来源： https://stackoverflow.com/questions/35150772/friend-function-template-with-default-template-argument

问题 This question already has answers here : How is it legal to reference an undefined type inside a structure? (7 answers) Closed last month . I recently came across this comment by @Paul Ogilvie: "You say "To define a pointer to a structure you only need to know the structure tag". In my experience that is unnecessary. Just declare a pointer_to_some_type and the compiler will reserve space for a pointer and does type checking on assignment. Only once you want dereference the pointer and access

问题 This question already has answers here : How is it legal to reference an undefined type inside a structure? (7 answers) Closed last month . I recently came across this comment by @Paul Ogilvie: "You say "To define a pointer to a structure you only need to know the structure tag". In my experience that is unnecessary. Just declare a pointer_to_some_type and the compiler will reserve space for a pointer and does type checking on assignment. Only once you want dereference the pointer and access

问题 This question already has answers here : How is it legal to reference an undefined type inside a structure? (7 answers) Closed last month . I recently came across this comment by @Paul Ogilvie: "You say "To define a pointer to a structure you only need to know the structure tag". In my experience that is unnecessary. Just declare a pointer_to_some_type and the compiler will reserve space for a pointer and does type checking on assignment. Only once you want dereference the pointer and access

问题 Code goes first: void foo(int x) { void bar(int); //is this forward-decl legal? bar(x); } void bar(int x) { //do stuff } In the code above, foo calls bar , usually I put the forward-decl of bar outside of foo , like this: void bar(int); void foo(int x) { bar(); } First, I think it's OK to put bar 's forward-decl inside foo , right? Second, consider this, if bar is a static function like this: static void bar(int x) { //do stuff } Then how should I forward-declare it? I mean should the forward

问题 If I have a normal class I can "inject" a non-free friend function inside the class. (That among other things can be only be found by ADL). case 1: class A{ double p_; friend double f(A const& a){return a.p_;} }; If instead this is a template class I can do: case 2: template<class T> class A{ double p_; friend double f(A const& a){return a.p_;} // apparently A const& is a synomyn for A<T> const& }; Now suppose that I need to implement f in terms of a class that needs to be defined later. I

问题 I've created a class that has a bunch of inherited classes (parent classes) so that I can use polymorphism but the problem is that there are two classes that are calling each other. So I need to forward declare them and I can forward declare one class but when I forward declare the inherited class the compiler says it can't change pointer from one to the other. Is there a way to make the forward declaration of the inherited class so that it states it inherits from it? Ex: class Shape; class

问题 Consider the following two scenarios (Edited just to complete the whole question and make it clearer) Case 1: (doesnt compile as rightly mentioned below) //B.h #ifndef B_H #define B_H #include "B.h" class A; class B { A obj; public: void printA_thruB(); }; #endif //B.cpp #include "B.h" #include <iostream> void B::printA_thruB(){ obj.printA(); } //A.h; #ifndef A_H #define A_H #include "A.h" class A { int a; public: A(); void printA(); }; #endif //A.cpp #include "A.h" #include <iostream> A::A()

问题 Consider the following two scenarios (Edited just to complete the whole question and make it clearer) Case 1: (doesnt compile as rightly mentioned below) //B.h #ifndef B_H #define B_H #include "B.h" class A; class B { A obj; public: void printA_thruB(); }; #endif //B.cpp #include "B.h" #include <iostream> void B::printA_thruB(){ obj.printA(); } //A.h; #ifndef A_H #define A_H #include "A.h" class A { int a; public: A(); void printA(); }; #endif //A.cpp #include "A.h" #include <iostream> A::A()