typedef-ing anonymous struct is a practice that pre-dates C++03 and is mainly oriented to retain compatibility with pre-C99 compilers. Given that this is 2011, and that both C++ and C are changed, I wonder why there is no more up-to-date version of such a library! If it is not in development anymore, you cannot “leave”, … Read more
It basically tells the compiler that the class RootViewController exists, without specifying what exactly it looks like (ie: its methods, properties, etc). You can use this to write code that includes RootViewController member variables without having to include the full class declaration. This is particularly useful in resolving circular dependencies – for example, where say … Read more
Did you forget to #include something? I got this after forgetting to #include <array> When using a std::array :^)
C++ Standard ISO/IEC 14882:2003(E) 7.3.1.2 Namespace member definitions Paragraph 3 Every name first declared in a namespace is a member of that namespace. If a friend declaration in a non-local class first declares a class or function (this implies that the name of the class or function is unqualified) the friend class or function is … Read more
A struct (without a typedef) often needs to (or should) be with the keyword struct when used. struct A; // forward declaration void function( struct A *a ); // using the ‘incomplete’ type only as pointer If you typedef your struct you can leave out the struct keyword. typedef struct A A; // forward declaration … Read more
If you will place your definitions in this order then the code will be compiled class Ball; class Player { public: void doSomething(Ball& ball); private: }; class Ball { public: Player& PlayerB; float ballPosX = 800; private: }; void Player::doSomething(Ball& ball) { ball.ballPosX += 10; // incomplete type error occurs here. } int main() { … Read more
Move doSomething definition outside of its class declaration and after B and also make add accessible to A by public-ing it or friend-ing it. class B; class A { void doSomething(B * b); }; class B { public: void add() {} }; void A::doSomething(B * b) { b->add(); }
A definition of a function is also a declaration of a function. The purpose of a declaring a function is to make it known to the compiler. Declaring a function without defining it allows a function to be used in places where it is inconvenient to define it. For example: If a function is used … Read more
A forward declaration is only really useful for telling the compiler that a class with that name does exist and will be declared and defined elsewhere. You can’t use it in any case where the compiler needs contextual information about the class, nor is it of any use to the compiler to tell it only … Read more
It’s explicitly legal. The rule is that the types used to instantiate a template in the standard library must be complete, unless otherwise specified. In the case of unique_ptr, §20.7.1/5 says “[…] The template parameter T of unique_ptr may be an incomplete type.” There are certain operations on the pointer which require a complete type; … Read more