为什么选择C ++中的dynamic_cast

Why to opt for dynamic_cast in C++

本问题已经有最佳答案，请猛点这里访问。

考虑以下代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57

#include <iostream>

using namespace std;

class Base{
int i;
public:
virtual bool baseTrue() {return true;}
Base(int i) {this->i=i;}
int get_i() {return i;}
};

class Derived : public Base{
int j;
public:
Derived(int i,int j) : Base(i) {this->j=j;}
int get_j() {return j;}
};

int main()
{
Base *bp;
Derived *pd,DOb(5,10);

bp = &DOb;

//We are trying to cast base class pointer to derived class pointer
cout << bp->get_i() << endl;
cout << ((Derived *)bp)->get_j() << endl;**//HERE1**

pd=dynamic_cast<Derived*> (bp); **//HERE2**
// If base class is not polymorphic
//throw error
//error: cannot dynamic_cast `bp' (of type `class Base*') to
//type `class Derived*' (source type is not polymorphic)

cout << pd->get_j() << endl;**//HERE2**

//Now we try to cast derived Class Pointer to base Class Pointer

Base *pb;
Derived *dp,Dbo(50,100);
dp = &Dbo;

cout << ((Base *)dp)->get_i() << endl;**//HERE3**
//cout << ((Base *)dp)->get_j() << endl;
//throws error Test.cpp:42: error: 'class Base' has no member named 'get_j'

pb = dynamic_cast<Base * > (dp); **//HERE4**
cout << pb->get_i() << endl; **//HERE4**
//cout << pb->get_j() << endl;
//throws error Test.cpp:47: error: 'class Base' has no member named 'get_j'

return 0;
}

输出

1
2
3
4
5
6
7

Gaurav@Gaurav-PC /cygdrive/d/Glaswegian/CPP/Test
$ ./Test
5
10
10
50
50

号

我的演员阵容(这里1行和这里2行)和(这里3行和这里4行)，这两者有什么区别？两者产生相同的输出，所以为什么要进行动态铸造？