FAQ Database Discussion Community


Forward Declaring and Dynamically Allocating an Array of Pointers of that Declared Class?

c++,forward-declaration
I have been having this problem all day with my C++ lab. As far as I can tell, I have everything working, except for this one clause that my professor has stipulated in our assignment: The order of class declarations in your source file is InventorySystem, InventoryItem, Product, eProduct. Since...

Understanding C struct

c,pointers,struct,function-pointers,forward-declaration
I'm trying to understand what's happening in the following C struct: /* EXCERPT from LINES 59-90 */ /* parse.h * Copyright (c) 2011, Peter Ohler * All rights reserved. */ typedef struct _ParseInfo { // used for the string parser const char *json; const char *cur; const char *end; //...

Forward declaration of type defined with `using`

c++,boost,forward-declaration
Let's assume I have such situation: //A.hpp #include "B.hpp" #include "C.hpp" #include "D.hpp" using A = boost::variant<B, C, D>; //B.hpp #include <memory> class A; using AA = std::unique_ptr<A>; This give me following error: error: typedef redefinition with different types ('boost::variant<B, C, D>' vs 'A') I can't omit #include's in A.hpp...

How do I forward declare an object in a class? (C++)

c++,class,forward-declaration
So basically, I have a global class and a player class. They are both defined in their ObjPlayer.h/ObjPlayer.cpp and same for the global. But how do I forward declare an instance of ObjPlayer within ObjGlobal? Here is what I have: (Defining the constructor, the class deceleration is elsewhere.) //Create all...

How to deal with namespaces in forward declarations? [duplicate]

c++,namespaces,forward-declaration
This question already has an answer here: How to forward declare a class which is in a namespace 1 answer Hi this is my straight forward question, because i dont know how to explain my question with some example. Question: How to deal with namescpaces in forward declarations where...

Is there a syntax for incomplete nested type without a forward declaration?

c++,c++11,nested,forward-declaration
The following program produces a diagnostic error. #include <memory> class Containing { // class Nested; // [1]: This line seems required. typedef std::shared_ptr<class Nested> Ptr; class Nested { Ptr & ptr (); void foo (const Ptr &p) { p->ptr() = ptr()->ptr(); // [2]: Error here without [1] } }; };...

How to declare an extern array of template class objects with a forward declared template class in C++?

c++,templates,extern,forward-declaration
Consider the following existing code (which compiles and executes as expected): /* File foo.h */ extern const struct Foo bar[]; /* Definition in foo.cpp */ struct Foo { Foo(int i) : Foo(bar[i]) {} int x; }; I now want to change Foo to a template class, such that: template <typename...

Change the meaning of code by replacement of forward declaration with include

c++,include,forward-declaration
Google C++ Style Guide states that In extreme cases, replacing an #include with a forward declaration can silently change the meaning of code. Can you please help me to find some examples? ...

Why are these global variables when they have namespace scope?

c++,namespaces,scope,global-variables,forward-declaration
In the following code, this is calling the variables in the globals.cpp namespace actual global variables. globals.h #ifndef GLOBALS_H_ #define GLOBALS_H_ namespace Constants { // forward declarations only extern const double pi; extern const double avogadro; extern const double my_gravity; } #endif globals.cpp namespace Constants { // actual global variables...

Declaration of cross-recursive rules

c++,recursion,static,boost-spirit,forward-declaration
I declared rules of my grammar as static const. That worked fine till I tried to use cross-recursive rules (rule1 is defined using rule2 which is defined using rule1). The source code still can be built, but segfaults on parsing source containing such cross-recursive case. Here's a simplified code of...

How do I get over this forward declaration error?

c++,forward-declaration
I'm trying to do a barebones example of a class A that provides callback methods to a dependent class B by passing a reference to itself. The best I've produced is the following: a.h #ifndef A_H #define A_H #include "b.h" namespace b { class ClassB; } namespace a { class...

Is there any way to declare mutual friend functions for two classes

c++,circular-dependency,forward-declaration,friend-function
class CDB; class CDM { public: friend CDB& CDB::Add(const CDM&); CDM& Add(const CDB&); }; class CDB { public: CDB& Add(const CDM&); friend CDM& CDM::Add(const CDB&); }; This code gives me the error : error C2027: use of undefined type 'CDB'. How to resolve this....

array of forward declared struct in another struct

c,struct,forward-declaration
I am trying to forward declare a struct A and define a struct B that contains an array of A. I am getting error stating 'incomplete type not allowed' This is what I have: struct A; struct B { // something struct A x[10]; // This where I get the...

No warning on deleting a forward declared pointer (Visual Studio)

c++,visual-studio-2012,memory-leaks,forward-declaration
Deleting forward declared pointers leads to undefined behavior. Examples: https://gist.github.com/jatinganhotra/4144778 http://stackoverflow.com/a/14382111/399908 However, my Visual Studio (VS2012) compiler doesn't warn me about it. Is this an unfixed VS2012 compiler bug? Did I disable (or never enable) the corresponding warning? Is this specific to some project setting? Visual Leak Detector hinted me...

Can't use std::unique_ptr with T being a forward declaration

c++,c++11,unique-ptr,forward-declaration
Now first, I am aware of the general issues with unique_ptr<> and forward declarations as in Forward declaration with unique_ptr? . Consider these three files: A.h #include <memory> #include <vector> class B; class A { public: ~A(); private: std::unique_ptr<B> m_tilesets; }; C.cpp #include "A.h" class B { }; A::~A() {...

Namespaces with multiple cyclic inclusion

c++,header,namespaces,include,forward-declaration
I've 3 classes that belong to a namespace "MyNS". "A" uses the "B" and "C", while both "B" and "C" use "A". Here are the structure of my headers: //mynamespace.h #ifndef SOMENAMESPACE_H #define SOMENAMESPACE_H namespace MyNS { class A; class B; class C; } #endif /*******************************************************/ //A.h #ifndef A_H #define...

Should one forward declare classes from a namespaced library?

c++,design,namespaces,forward-declaration
I'm designing a C++ library that will be placed inside a namespace. If the users of my library only need a forward declaration of one of my classes and since you can't do forward declarations of things inside a namespace, e.g. class ns_name::class_name;, should I tell them to include the...

Forward declarated class with default value

c++,default-value,forward-declaration
I have a forward declaration but want to have a instatance of the forward declarated class as default value. So my code looks more or less like this: bar.h class Foo; class Bar { public: Bar(); void test(Foo foo = Foo(7)); } and foo.h class Foo { public: Foo(int val);...

Can't access object variables passed in a std callback

c++,forward-declaration,dereference
I have a callback function (ouside my class) which i'm passing a BassMusicPlayer class object as parameter. If do a breakpoint inside it, i can see all the variables and methods in 'self'. If i try to read/print those values, it won't compile and will give error C2027: use of...

Trying to befriend a function of Derived in Base - Why doesn't it work?

c++,inheritance,friend,forward-declaration,friend-function
My first post here. I have two classes - Base and Derived (derived publicly from Base). In Derived, I have a function printAsFriend. Compiler is unhappy with this. Why? Methods in other classes can be befriended. Why doesn't it work with a derived class? It works OK if I remove...

Function definition preceeds declaration in namespace

c++,namespaces,forward-declaration
The following bit of code, in which a function definition predeeds its declaration, compiles in VS .NET 2008 and Cygwin gcc 4.8.2. Is it legal? namespace N { int init() // Definition appears first { return 42; } } namespace N { int init(); // followed by declaration const int...

Assigning a function pointer with a forward-declared prototype in Nim

function-pointers,forward-declaration,nim
I want to assign a Window Procedure to a Window Class structure: var wndClass : WNDCLASS; wndClass.lpszClassName = CLASSNAME; wndClass.lpfnWndProc = WndProc; wndClass.hInstance = hInstance; I can't assign WndProc yet because it hasn't been declared. When I use a forward declaration (described here): proc WndProc(hWnd: HWND; msg: WINUINT; wParam: WPARAM;...