error C2248: 'CObject::operator =' : cannot access private member declared in class 'CObject'

error C2248: 'CObject::operator =' : cannot access private member declared in class 'CObject'

先看一段示例代码：

1 #define C2248_SWITCH 0
2
3 struct A
4 {
5 int a;
6 };
7
8 struct B
9 {
10 CArray<A, A&> b;
11 #if C2248_SWITCH
12 const B& operator=(const B& rhs)
13 {
14 if(this != &rhs)
15 {
16 b.RemoveAll();
17 b.Append(rhs.b);
18 b.FreeExtra();
19 }
20
21 return *this;
22 }
23 #endif
24 };
25
26 typedef CArray<B, B&> C;
27
28 void test()
29 {
30 B b;
31 C c;
32 c.Add(b); // C2248, C2248_SWITCH is defined as 0.
33 }
34
编译时产生如下信息：

1 Compiling


2 CArrayTest.cpp
3 c:/program files/microsoft visual studio 8/vc/atlmfc/include/afxtempl.h(272) : error C2248: 'CObject::operator =' : cannot access private member declared in class 'CObject'
4 c:/program files/microsoft visual studio 8/vc/atlmfc/include/afx.h(559) : see declaration of 'CObject::operator ='
5 c:/program files/microsoft visual studio 8/vc/atlmfc/include/afx.h(529) : see declaration of 'CObject'
6 This diagnostic occurred in the compiler generated function 'CArray<TYPE,ARG_TYPE> &CArray<TYPE,ARG_TYPE>::operator =(const CArray<TYPE,ARG_TYPE> &)'
7 with
8 [
9 TYPE=A,
10 ARG_TYPE=A &
11 ]从以上的编译信息line9, line10可以看出是struct B默认的operator=运算符函数(由编译器自动产生)出现了问题。因为struct B有一个CArray<A, A&>的成员变量，而CArray<A, A&>类的operator=是private类型(它继承自CObject::operator=，且被定义为private类型)。所以我们要在struct B中重载operator=运算符，且把它声明为public类型(struct中的成员变量和成员函数默认就是public类型，所以不用显式的指明public).


在本示例代码中，只需把C2248_SWITCH定义为1即可。 由本例可以看出，如果我们的类/结构体中有CArray(或CList等其他的派生自CObject类)的成员变量，我们最好添加上一个public类型的operator=运算赋重载函数。