Page 114 - DCAP404 _Object Oriented Programming
P. 114
Unit 5: Static Members
{ Notes
int iMsgNo = 1; // assign arbitrary value as message number
strcpy( BufferedIO::BufferedInput::message,
rgszMessage[iMsgNo] );
return iMsgNo;
}
int main()
{
}
The preceding code shows the function GetExtendedErrorStatus declared as a friend function. In
the function, which is defined in file scope, a message is copied from a static array into a class
member. Note that a better implementation ofGetExtendedErrorStatus is to declare it as:
int GetExtendedErrorStatus( char *message )
With the preceding interface, several classes can use the services of this function by passing a
memory location where they want the error message copied.
Task The friend function has access to the private data member of the Point object it
receives as a parameter. Analyse.
5.4.3 Friend Function in Local Classes
The name of a friend function or class first introduced in a friend declaration is not in the scope
of the class granting friendship (also called the enclosing class) and is not a member of the class
granting friendship.
The name of a function first introduced in a friend declaration is in the scope of the first nonclass
scope that contains the enclosing class. The body of a function provided in a friend declaration
is handled in the same way as a member function defined within a class. Processing of the
definition does not start until the end of the outermost enclosing class. In addition, unqualified
names in the body of the function definition are searched for starting from the class containing
the function definition.
If the name of a friend class has been introduced before the friend declaration, the compiler
searches for a class name that matches the name of the friend class beginning at the scope of the
friend declaration. If the declaration of a nested class is followed by the declaration of a friend
class with the same name, the nested class is a friend of the enclosing class.
The scope of a friend class name is the first nonclass enclosing scope. For example:
class A {
class B { // arbitrary nested class definitions
friend class C;
};
};
is equivalent to:
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