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Questions tagged [friend]

In object-oriented programming, friend refers to a method or class that has access to some non-public aspects of a particular class.

In object-oriented programming, friend refers to a method or class that has access to some non-public aspects of a particular class.

Different programming languages use the friend keyword differently. Make sure it is clear which language you are asking about.

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Is friendship inherited in C++?

Suppose I have a Base class: class Base { friend SomeOtherClass; }; And there is another (different) class that inherits from Base: class AnotherClass : public Base {} Is friendship inherited as well?
tunnuz
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c++ friend function - operator overloading istream >>

My question is in regards to friend functions as well as overloading the << and >>. From my understanding I thought friend functions could (and should) access private member variables directly. However in the case I have here the compiler would only…
user399415
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I believe clang erroneously allows inline friend function access to data in an enclosing scope. Both gcc and vs2013 reject this code

The friend function f doesn't have access to a private member of the enclosing class A. #include class A{ const static int p = 1; class B { friend void f() { std::cout << p << '\n'; std::cout << q…
Belloc
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Friend lookup exception from template-id?

Consider the following clause in [namespace.memdef]/3: If the name in a friend declaration is neither qualified nor a template-id and the declaration is a function or an elaborated-type-specifier, the lookup to determine whether the entity has…
Barry
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Friend function is unable to construct a unique pointer of the class

I have a certain design strategy where the constructor of my class is private and can only be constructed by friends of the class. Inside the friend function, I am trying to create a unique_pointer of my class using std::make_uniquebut it doesn't…
Abhijit
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How can I remove/refactor a «friend» dependency declaration properly?

The background of this question is based on a practical sample where I wanted to remove a «friend» dependency from a pair of classes that are used to manage read/write locked access to a shared resource. Here's an abstraction of the original…
πάντα ῥεῖ
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Declaring main as friend considered harmful?

Discussion I know that main can be a friend of a class: #include class foo { friend int main(); int i = 4; }; int main() { foo obj; std::cout << obj.i << std::endl; } LIVE DEMO However, I feel that although this is perfectably…
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class friend function inside a namespace

Im trying to define a class friend function outside the namespace like this: namespace A{ class window{ private: int a; friend void f(window); }; } void f(A::window rhs){ cout << rhs.a << endl; } Im getting an error said that there…
AlexDan
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Is it possible to mark an alias template as a friend?

Imagine we have this code: template class Element {}; template class Util { public: template using BeFriend = Element; }; Is it possible to mark BeFriend as a friend ? (Of Util, or any other…
Ad N
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How to make the lambda a friend of a class?

Let's say, I have a class: class A { int a; }; And I have a lambda: auto function = [](A* a) { a->a; // <== gives an error in this line. }; function(new A); Is there any way to use a private member/method inside a lambda? - It's not…
abyss.7
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friend class declaration and using directive

Is the following example well-formed? namespace N { class A; } using namespace N; class B { int i; friend class A; }; namespace N { class A { B m; int get() { return m.i; } }; } This example compiled…
Mitsuru Kariya
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C++ How to specify all friends of a templated class with a default argument?

To define a friend of a templated class with a default argument, do you need to specify all friends as in the code below (which works)? // Different class implementations enum ClassImplType { CIT_CHECK, CIT_FAST, CIT_GPU, CIT_SSE, CIT_NOF_TYPES }…
Anne van Rossum
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Granting friendship to constructor/destructor of template class specialization - works under C++17, but fails under C++20

I have found a situation where code compiles successfully under C++17, but FAILS under C++20. This blocks us from upgrading our existing code design to the newer standard. Why doesn't this compile under C++20? It seems like a weird breach of…
Giffyguy
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Can a friend class object access base class private members on a derived class object?

I'm surprised that the code below compiles. It seems that a class befriended to the (publicly inherited) base class can access a member of the base class provided an instance of the derived class. If the inheritance is changed to private then…
Hemant Sharma
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The member function Outer::f() is not a friend of class Outer::Inner. Why?

According to clang, gcc and vs2013, the function Outer::f is not a friend of the class Outer::Inner. struct Outer { void f() {} class Inner { friend void f(); static const int i = 0; }; }; void f() { int i =…
Belloc
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