转载自：
C++/面试 - 四种类型转换(cast)的关键字 详解 及 代码 - c++语言程序开发技术文章_c++编程 - 红黑联盟
http://www.2cto.com/kf/201402/277584.html
四种类型转换(cast)的关键字 详解 及 代码
C++中常见的面试题.
题目: 关于C++中, 四种类型转换的关键字, 的详解, 也可以给出代码, 判断输出 或 判断哪些代码有误.
答案及范例如下:
四种关键字: const_cast, 常量性转除;dynamic_cast, 向下安全转型;reinterpret_cast, 重新解释转型; static_cast, 静态转型;
1. const_cast, 常量性转除:
主要对变量的常量性(const)进行操作, 移除变量的常量性, 即可以被非常量指向和引用, 详见代码;
2. dynamic_cast, 向下安全转型:
主要应用于继承体系, 可以由 指向派生类的基类部分的指针, 转换指向派生类或指向兄弟类;
static_cast只能转换为指向派生类;
3. reinterpret_cast, 重新解释转型:
主要是对2进制数据进行重新解释(re-interpret),不改变格式, 而static_cast会改变格式进行解释;
如由派生类转换基类, 则重新解释转换, 不改变地址, 静态转换改变地址;
4. static_cast, 静态转型:
主要是数据类型的转换, 还可以用于继承;
代码如下:
|
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
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
|
/* * cppprimer.cpp * * Created on: 2014.2.10 * Author: Spike *//*eclipse cdt, gcc 4.8.1*/#include <iostream>/*常量性移除指针详解*/struct S { S() : value(0) {} int value;};void CastConst (void){ const S s; std::cout << s.value = << s.value << std::endl; //S* ps = &s; //error, 指向常量 S* ps = const_cast<s*>(&s); ps->value = 1; std::cout << s.value = << s.value << std::endl; //S& rs = s; //error, 引用常量 S& rs = const_cast<s&>(s); rs.value = 2; std::cout << s.value = << s.value << std::endl;}/*安全向下转型*/struct B /*基类B*/ { virtual void f() { std::cout << Base::f << std::endl; } void thisf() { std::cout << Base::thisf << std::endl;} virtual ~B() {}};struct B2 /*基类B2*/ { virtual void g() { std::cout << Base2::g << std::endl; } void thisg() { std::cout << Base2::thisg << std::endl;} virtual ~B2() {}};struct D : public B, public B2 /*派生类D*/ { virtual void f() { std::cout << Derived::f << std::endl; } virtual void g() { std::cout << Derived::g << std::endl; } virtual ~D() {}};void CastDynamic (void){ B* pB_D = new D; pB_D->f(); //pD->g(); //error, 只包含B部分 D *pD_D = dynamic_cast<d*>(pB_D); //转换为派生类 pD_D->g(); B2* pB2_D = dynamic_cast<b2*>(pB_D); //转换为兄弟类 pB2_D->g(); D *pD_Ds = static_cast<d*>(pB_D); pD_Ds->g(); //B2* pB2_Ds = static_cast<b2*>(pB_D); //error, 不能转换为兄弟类}/*重新解释转型*/struct rA { int m_a; };struct rB { int m_b; };struct rC : public rA, public rB {};void CastReinterpret (void){ int *i= new int; *i = 10; std::cout << *i = << *i << std::endl; std::cout << i = << i << std::endl; double *d=reinterpret_cast<double*> (i); std::cout << *d = << *d << std::endl; std::cout << d = << d << std::endl; rC c; std::cout << &c = << &c << std::endl << reinterpret_cast<rb*>(&c) = <<reinterpret_cast<rb*>(&c) << std::endl << static_cast <rb*>(&c) = << static_cast <rb*>(&c) << std::endl << reinterpret_cast<ra*>(&c) = <<reinterpret_cast<ra*>(&c) << std::endl << static_cast <ra*>(&c) = << static_cast <ra*>(&c) << std::endl << std::endl;}int main (void){ std::cout << std::endl << 常量性转除: << std::endl; CastConst(); std::cout << std::endl << 安全向下转型: << std::endl; CastDynamic(); std::cout << std::endl << 重新解释转型: << std::endl; CastReinterpret();}</ra*></ra*></reinterpret_cast<ra*></ra*></rb*></rb*></reinterpret_cast<rb*></rb*></double*></b2*></d*></b2*></d*></s&></s*></iostream> |
输出:
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
|
常量性转除:s.value = 0s.value = 1s.value = 2安全向下转型:Derived::fDerived::gDerived::gDerived::g重新解释转型:*i = 10i = 0x471718*d = 2.55917e-307d = 0x471718&c = 0x22feb0reinterpret_cast<rb*>(&c) = 0x22feb0static_cast <rb*>(&c) = 0x22feb4reinterpret_cast<ra*>(&c) = 0x22feb0static_cast <ra*>(&c) = 0x22feb0</ra*></ra*></rb*></rb*>
|