Friends
A friend is permitted full access to private and protected members. A friend can be a function, function template, or member function, or a class or class template, in which case the entire class and all of its members are friends.
Use the friend
specifier to
declare a friend in the class granting friendship. Note that friendship
is given, not taken. In other words, if class A contains the declaration
friend
class
B;
, class B can access the private members of A, but A has no
special privileges to access B (unless B declares A as a friend).
By convention, the friend
specifier is usually first, although it can appear in any order with
other function and type specifiers. The friend
declaration can appear anywhere in the
class; the access level is not relevant.
You cannot use a storage class specifier in a friend declaration. Instead,
you should declare the function before the class definition (with the
storage class, but without the friend
specifier), then redeclare the function in the class definition (with
the friend
specifier and without the
storage class). The function retains its original linkage. If the
friend
declaration is the first
declaration of a function, the function gets external linkage. (See
Chapter 2 for more information
about storage classes and linkage.) For example:
class demo; static void func(demo& d); class demo { friend void func(demo&); ...
Friendship is not transitive—that is, the friend of my friend is not my friend (unless I declare so in a separate ...
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