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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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friend and template in C++

I have a big problem in my C++ Code example. There is something wrong with 'friend' and the 'template'. Error Messages: Matrix.h:26:79: warning: friend declaration 'std::ostream& matrixClass::operator<<(std::ostream&, const…
Peter Herrlich
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Overloading operator<< - must be a binary operator

What's the error here? I reviewed prior Q&A, but all those coders appear to have made other errors when overloading <<. When I try it, QT Creator gives this error: overloaded 'operator<<' must be a binary operator (has 3 parameters), referring to…
NAR
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Friendship in nested classes C++

I am trying to understand concept of friendship in nested classes but I am not getting the concept properly. I have written a sample program to understand it but the program is not working #include using namespace std; class…
Mayank Jain
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Incomplete type in friend function

This is a mcve of my code: (if it matters, Options_proxy and Options have constexpr ctors). I am aware it's still far from simple, but couldn't simplify it more while still exhibiting the error: template struct Options_proxy : Impl { …
bolov
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Friends confusion

$11.4/5 - "[...]A friend function defined in a class is in the (lexical) scope of the class in which it is defined[...]" What does this statement mean? struct A{ typedef int MYINT; void f2(){f();} // Error, 'f' is undefined …
Chubsdad
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Friend template function declared inside template class causing undefined symbol link error

I have been banging my head against this for a couple of days, looking it up and also looking for similar code in open source projects: can't really find what I'm doing incorrectly. Essentially, given the code below (distilled to its…
Marco Massenzio
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Calling friend function defined in struct requires forward declaration?

While reading Karlsson's Beyond the C++ Standard the author defined the friend function intrusive_ptr_add_ref in the body of class reference_counted (see pg 36). That function is called automatically using Argument Dependent Lookup at the proper…
themis
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Unused friend class in C++

Is there a way to detect (for instance with compiler warning) if classes are declared friend but do not access private members, ie. when friendship is useless?
Giovanni Funchal
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template friend functions of template class

I have the following template class and template function which intends to access the class' private data member: #include template class MyVar { int x; }; template void printVar(const MyVar& var) { …
timrau
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Friend functions and static data members

How is unqualified name lookup being performed for names using within the friend's function body? Let's consider the following code: #include void foo(); class A { friend void foo(){ std::cout << a << std::endl; } static int…
user2953119
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How to befriend a templated class's constructor?

Why does class A; template class B { private: A* a; public: B(); }; class A : public B { private: friend B::B(); int x; }; template B::B() { a = new A; a->x = 5; } int…
Kyle
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Set a project default for VB.NET projects so that the default Modifiers property for controls is Private

Is it possible to set a project default for VB.NET winforms projects so that the default Modifier for controls added to winforms is Private (not Friend)? I know there's a "modifiers" property in the properties window so I can set it for each…
Darren
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operator << friend function and templates

This is my code: mov.h #include template< class T> class Movie { public: Movie(T in) { a = in; } friend std::ostream& operator<<(std::ostream& os, const Movie& movie); private: T a; }; template
user11001
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When is "already a friend" warning useful?

I have code which uses a preprocessor-heavy framework to generate some utility classes. Apparently, some of the macros result in the same friend declaration being included twice in a class, something like this: class Friendly { // ::: friend…
Angew is no longer proud of SO
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What does `template friend class Foo` mean?

I'm exploring the boost::iterator_facade and came across this bit of code: friend class boost::iterator_core_access; template friend class Iterator; What does the second line mean? I'm familiar with friend classes, but I don't think…
vmrob
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