Exer19_03_04.cpp

// Warning: not every compiler could compile this.
#include <iostream>
#include <typeinfo>
using std::cout;
using std::endl;
class A {
public:
    A() = default;
    virtual ~A() = default;
};
class B : public A {
public:
    B() = default;
    ~B() = default;
};
class C : public B {
public:
    C() = default;
    ~C() = default;
};
class D : public B, public A {
public:
    D() = default;
    ~D() = default;
};
int main()
{
    // exercise 19.3
    // (a)
    A *pa1 = new C;
    if(B *pb1 = dynamic_cast<B*>(pa1)) {
        cout << "(a): cast succeeds!" << endl;
    } else {
        cout << "(a): cast fails!" << endl;
    }
    // (b)
    B *pb2 = new B;
    // fail, dynamic type of pb2 is not C or derived class of C
    if(C *pc1 = dynamic_cast<C*>(pb2)) {
        cout << "(b): cast succeeds!" << endl;
    } else {
        cout << "(b): cast fails!" << endl;
    }
    // (c)
    A *pa2 = new D;
    if(B *pb3 = dynamic_cast<B*>(pa2)) {
        cout << "(c): cast succeeds!" << endl;
    } else {
        cout << "(c): cast fails!" << endl;
    }

    // exercise 19.4
    try {
        C &rc1 = dynamic_cast<C&>(*pa1); // ok: dynamic type of pa1 is C
        C &rc2 = dynamic_cast<C&>(*pa2); // error: dynamic type of pa2 is not C
                                         // or its derived class
    } catch(std::bad_cast e) {
        cout << e.what() << endl;
    }
    return 0;
}
// ******compile info of g++******
// Exer19_03.cpp:20:7: warning: direct base 'A' inaccessible in 'D' due to ambiguity
//  class D : public B, public A {
//        ^
// Exer19_03.cpp: In function 'int main()':
// Exer19_03.cpp:43:15: error: 'A' is an ambiguous base of 'D'
//   A *pa2 = new D;
//                ^

// ******compile info of clang++******
// Exer19_03.cpp:20:21: warning: direct base 'A' is inaccessible due to ambiguity:
//     class D -> class B -> class A
//     class D -> class A [-Winaccessible-base]
// class D : public B, public A {
//                     ^~~~~~~~
// Exer19_03.cpp:43:11: error: ambiguous conversion from derived class 'D' to base
//       class 'A':
//     class D -> class B -> class A
//     class D -> class A
//         A *pa2 = new D;
//                  ^~~~~
// 1 warning and 1 error generated.

// ******compile info of cl******
// 用于 x86 的 Microsoft (R) C/C++ 优化编译器 18.00.40629 版版权所有(C) Microsoft C
// orporation。  保留所有权利。
//
// Exer19_03.cpp
// Exer19_03.cpp(19) : warning C4584: “D”: 基类“A”已是“B”的基类
//         Exer19_03.cpp(4) : 参见“A”的声明
//         Exer19_03.cpp(9) : 参见“B”的声明