Can a C++ class have an object of self type?

　　A class declaration can contain static object of self type，it can also have pointer to self type，but it can not have a non-static object of self type。

　　例如，下面的程序可运行。

 1 // A class can have a static member of self type
 2 #include<iostream>
 3
 4 using namespace std;
 5
 6 class Test
 7 {
 8     static Test self;  // works fine
 9
10     /* other stuff in class*/
11
12 };
13
14 int main()
15 {
16     Test t;
17     getchar();
18     return 0;
19 }

　　下面的程序也可运行。

 1 // A class can have a pointer to self type
 2 #include<iostream>
 3
 4 using namespace std;
 5
 6 class Test
 7 {
 8     Test *self;  // works fine
 9
10     /* other stuff in class*/
11
12 };
13
14 int main()
15 {
16     Test t;
17     getchar();
18     return 0;
19 }

　　但是，下面的程序会产生编译错误"field `self’ has incomplete type“。

　　在VC 6.0下会产生编译错误"error C2460: 'self' : uses 'Test', which is being defined"。

 1 // A class can not have a non-static member of self type
 2 #include<iostream>
 3
 4 using namespace std;
 5
 6 class Test
 7 {
 8     Test self;  // works fine
 9
10     /* other stuff in class*/
11
12 };
13
14 int main()
15 {
16     Test t;
17     getchar();
18     return 0;
19 }

　　If a non-static object is member then declaration of class is incomplete and compiler has no way to find out size of the objects of the class.

　　如果在类的声明中，non-static对象是该类的成员，若该non-static对象是incomplete，那么，编译器没有办法获取该类对象的大小。

　　

　　static variables do not contribute to the size of objects. So no problem in calculating size with static variables of self type.

　　由于类的对象的大小是由non-static数据成员构成的，当然， 这里仅仅是无继承的、无虚函数的类。所以static数据成员不构成类的对象的大小，因此，当类的声明中包含有该类的static objects时是没有问题的。

　　For a compiler, all pointers have a fixed size irrespective of the data type they are pointing to, so no problem with this also.

　　对于编译器而言，所有类型的指针有固定的大小（32位机器下4字节），与指针所指对象的数据类型没有关系，所以类声明中包含自身类型的指针是没有问题的。

　　

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　　2013-11-25　　20:14:30