多重继承的内存布局、数据成员指针偏移量及空指针

 C++ Code 

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struct Base1 {int val10;int val11;}; struct Base2 {int val20;}; struct Derived : public Base2, Base1 {int val;}; // 多重继承下，数据的布局 /*  *  @Func : 在VC环境下，测试多重继承的内存布局，及数据成员指针              Address 0: 20              Address 4: 10              Address 8: 11              Address 12: 3              &Base1::val10 = 00000000              &Base1::val11 = 00000004              &Base2::val20 = 00000000              &Derived::val10 = 00000000              &Derived::val20 = 00000000              &Derived::val11 = 00000004              &Derived::val = 0000000C              空数据成员指针 地址 = 0019F65C，值 = FFFFFFF              &Base1::val10 地址 = 0019F650，值 = 00000000              &Base1::val11 地址 = 0019F644，值 = 00000004              &Base2::val20 地址 = 0019F638，值 = 00000000              &Derived::val10 地址 = 0019F62C，值 = 000000              &Derived::val11 地址 = 0019F620，值 = 000000              &Derived::val20 地址 = 0019F614，值 = 000000              &Derived::val 地址 = 0019F608，值 = 0000000C  * (1)从地址的值来看，内存布局为Base2→Base1→Derived；(2) 基类变量的数据成员指针具有相同的偏移，为0。与书中描述不符  * (3) 空数据成员指针的值为FFFFFFFF，而数据成员函数的指针则是偏移量。由于对空数据成员指针的特殊赋值，使得偏移量不需要+1  *  * @说明：(1)对于多重继承的内存布局，VC的结果与书中的相同；(2)对于数据成员指针的偏移，VC的结果与书中出入很大  */ void Test_DataMember_Pointer(){     Derived d; d.val = 3;     d.val10 = 10; d.val11 = 11;     d.val20 = 20;     // 通过观察值得到内存布局     printf("Address 0: %d \n", *((int*)(int(&d)))); // 从测试结果来看，首地址为Base2::val20     printf("Address 4: %d \n", *((int*)(int(&d)+4))); // 从测试结果来看，该地址为Base1::val10     printf("Address 8: %d \n", *((int*)(int(&d)+8))); // 从测试结果来看，该地址为Base1::val11     printf("Address 12: %d \n\n", *((int*)(int(&d)+12))); //从测试结果来看，该地址为Derived::val     // 数据成员指针偏移量     printf("&Base1::val10 = %p \n", &Base1::val10);     printf("&Base1::val11 = %p \n", &Base1::val11);     printf("&Base2::val20 = %p \n", &Base2::val20);     printf("&Derived::val10 = %p \n", &Derived::val10); // 从测试结果来看，&Derived::val10、&Derived::val11与&Derived::val20的偏移相同，均为0     printf("&Derived::val20 = %p \n", &Derived::val20);     printf("&Derived::val11 = %p \n", &Derived::val11);      printf("&Derived::val = %p \n\n", &Derived::val); // 偏移12     // 空数据成员指针与数据成员指针的比较     int CPoint::*p00 = 0;     int Base1::*p10 = &Base1::val10;     int Base1::*p11 = &Base1::val11;     int Base2::*p20 = &Base2::val20;     int Derived::*p30 = &Derived::val10;     int Derived::*p31 = &Derived::val11;     int Derived::*p32 = &Derived::val20;     int Derived::*p33 = &Derived::val;     printf("空数据成员指针 地址 = %p，值 = %p \n", &p00, p00);     printf("&Base1::val10 地址 = %p，值 = %p \n", &p10, p10);     printf("&Base1::val11 地址 = %p，值 = %p \n", &p11, p11);     printf("&Base2::val20 地址 = %p，值 = %p \n", &p20, p20);     printf("&Derived::val10 地址 = %p，值 = %p \n", &p30, p30);     printf("&Derived::val11 地址 = %p，值 = %p \n", &p31, p31);     printf("&Derived::val20 地址 = %p，值 = %p \n", &p32, p32);     printf("&Derived::val 地址 = %p，值 = %p \n", &p33, p33); }