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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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Making default constructor private in Qt custom object

I'm reading this Qt doc page about custom types, and it states the following: The default constructor, copy constructor and destructor are all required, and must be public, if the type is to be integrated into the meta-object system. Suppose I…
ABCplus
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Template friend function and return type deduction

Note: This question is really close to Return type deduction for in-class friend functions, but I did not find the answer to my problem there. Tested with clang 3.4 with std=c++1y and clang 3.5 with std=c++14 and std=c++1z This code…
Bérenger
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C++11 Declaring factory a friend of base class

I'm trying to create a factory for derived classes. I only want the factory to be able to create instances of the derived classes so I've made the base constructor protected; the derived classes just use the base class constructors so their…
jlconlin
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Is a local class in a method of a class a friend of this class?

I have an outer class A. It has a method A::fun. In this method, it has a local or inner class B. My question is: Is B a friend of A? I think it is not. Is it right? If so, I think let class B a friend of A is very beneficial since B can access to…
user1899020
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Friend function from a templated class

I have a class like this: #include "Blarg.h" // ... class Foo : public Bar { // ... static double m_value; // ... }; And another one like this: template class Blarg : public Bar { // ... void SetValue(double…
norman
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Partial specialization and friendship

Suppose you have class A like this: template class A; And class B like this: template class B; And now you want both classes be friends when T is the same type, is this possible? So for example A is…
user3624760
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Class friendship - a puzzle

I am an object-oriented programming enthusiast at a beginner level. I have encountered the following puzzle: class A { }; class B { protected: friend class A; }; class C { public: friend class B; }; Referring to the sample code…
Prz3m3k
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Friendship not inherited - what are the alternatives?

I have written/am writing a piece of physics analysis code, initially for myself, that will now hopefully be used and extended by a small group of physicists. None of us are C++ gurus. I have put together a small framework that abstracts the…
Anthony
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Template parameter as a friend

In C++03 the following is illegal, although some compilers support it. template class X { friend T; }; Has this been legalized in C++11? (Sorry, didn't have time to read the draft myself, just hoping someone knows this)
Armen Tsirunyan
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Difference of C++17 and C++20 in template friend function with unary and binary operators

I have the following MWE in C++20 with clang++ -std=c++2a, in which I defined in-class unary - operator and friend-ed binary - operator: template class vec; template vec operator-(const vec&, const…
Jay Lee
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recursive friend classes

Is there any way around this: class B; class C { public: C() { } private: int i; friend B::B(); }; class B { public: B() { } private: int i; friend C::C(); }; Gives error: prog.cpp:8: error: invalid use of incomplete type…
BCS
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g++ issues incomprehensible warning

system.h: #include namespace ss { class system { private: // ... public: // ... friend std::ostream& operator<< (std::ostream& out, const system& sys); }; } system.cpp: #include "system.h" std::ostream&…
Danish
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Friend functions of a class template

I have a class template Foo. I'd like to implement a non-member function Bar that takes two Foos and returns a Foo. I want Bar to be a non-member because it will be more natural for callers to write Bar(f1, f2) than f1.Bar(f2). I also want Bar…
Adrian McCarthy
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Regarding friend function definition and namespace scopes

I was reading this blog post section, and I tried to play around with the snippet that was provided. namespace N { // 2 class A { friend void f(A) {} // 1 }; } If I understood correctly, the definition in // 1 will inject the name f where // 2 is…
Dante
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Grant access to private constructor without friends?

I am working on some code, where I encountered a situation similar to this one: struct Bar; struct Foo{ friend struct Bar; private: Foo(){} void f(){} void g(){} }; struct Bar { Foo* f; Bar() { f = new Foo();} ~Bar() {…
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