Softwareentwicklung in C++ - ASC

248 9. Klassen in C++
suchen müssen, die von Außenstehenden verursacht werden, denen Zugriffe
gestattet wurden, vor denen man sich üblicherweise aus gutem Grund
schützt.
Um für die Fälle, bei denen es wirklich unumgänglich ist, zu wissen, wie
man den Zugriff für Außenstehende gestattet, werfen wir einen Blick auf das
folgende Beispiel (friend_demo.cpp):
1 // friend demo . cpp − demo f o r the use o f the f r i e n d d e c l .
2
3 #include
4
5 using std : : cout ;
6 using std : : endl ;
7
8 //−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
9 /∗
10 ∗ MyClass
11 ∗
12 ∗ j u s t a demo c l a s s
13 ∗
14 ∗/
15
16 class MyClass
17 {
18 friend class MyGoodFriend ;
19 friend void myGoodFriendFunction ( MyClass &obj ) ;
20 private :
21 int my private member ;
22 int myPrivateMethod ( ) { return ( my private member ) ; }
23 public :
24 MyClass ( ) { my private member = 2 0; }
25 } ;
26
27 //−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
28 /∗
29 ∗ MyDerivedClass
30 ∗
31 ∗ j u s t another demo c l a s s
32 ∗
33 ∗/
34
35 class MyDerivedClass : public MyClass
36 {
37 private :
38 int really private member ;
39 int reallyPrivateMethod ( ) { return ( really private member ) ; }
40 public :
41 MyDerivedClass ( ) { really private member = 7 0; }
42 } ;
43
44 //−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
45 /∗
46 ∗ MyGoodFriend
47 ∗
48 ∗ j u s t a demo f o r a f r i e n d c l a s s f o r MyClass
49 ∗
50 ∗/
51
52 class MyGoodFriend
53 {
54 public :
55 void showAccessToMyClass ( MyClass &obj )