C++ 类型转换

标签：c++   类型转换   

该运算符用来修改类型的const或volatile属性。除了const 或volatile修饰之外， type_id和expression的类型是一样的。

#include <stdio.h>

using namespace std;

struct Data{
    int value;
};

int main(int argc, _TCHAR* argv[])
{
    const Data data1 = {10};
    //data1.value = 15; //error C3892: “data1”: 不能给常量赋值
    Data &data2 = const_cast<Data &>(data1);
    data2.value = 20;
    printf("data1.value = %d data2.value = %d\n",data1.value,data2.value);

    const int a = 10;
    int *b = const_cast<int*>(&a);
    *b = 20;
    printf("a = %d b == &a is %d\n",a,b == &a);

    system("pause");

    return 0;
}

class BaseClass {
public:
int m_iNum;
virtualvoid foo(){}; //基类必须有虚函数。保持多台特性才能使用dynamic_cast
};

class DerivedClass: public BaseClass {
public:
char*m_szName[100];
void bar(){};
};

BaseClass* pb =new DerivedClass();
DerivedClass *pd1 = static_cast<DerivedClass *>(pb); //子类->父类，静态类型转换，正确但不推荐
DerivedClass *pd2 = dynamic_cast<DerivedClass *>(pb); //子类->父类，动态类型转换，正确

BaseClass* pb2 =new BaseClass();
DerivedClass *pd21 = static_cast<DerivedClass *>(pb2); //父类->子类，静态类型转换，危险！访问子类m_szName成员越界
DerivedClass *pd22 = dynamic_cast<DerivedClass *>(pb2); //父类->子类，动态类型转换，安全的。结果是NULL

#include <stdio.h>

using namespace std;

class A
{
public:
    int m_a;
};

class B
{
public:
    int m_b;
};

class C:public A,public B
{

};



int main(int argc, _TCHAR* argv[])
{
    
    C* c = new C();
    c->m_a = 1;
    c->m_b = 2;

    A* a1 = static_cast<A*>(c);
    A* a2 = reinterpret_cast<A*>(c);

    B* b1 = static_cast<B*>(c);
    B* b2 = reinterpret_cast<B*>(c);

    printf("c = %p,a1 = %p,b1 = %p\n",c,a1,b1);
    printf("c = %p,a2 = %p,b2 = %p\n",c,a2,b2);

    printf("a1.m_a = %d, b1.m_b = %d\n",a1->m_a,b1->m_b);
    printf("a2.m_a = %d, b2.m_b = %d\n",a2->m_a,b2->m_b);

    system("pause");
    return 0;
}

运行结果：

c = 00392950,a1 = 00392950,b1 = 00392954
c = 00392950,a2 = 00392950,b2 = 00392950
a1.m_a = 1, b1.m_b = 2
a2.m_a = 1, b2.m_b = 1

reinterpret_cast的一个使用例子：

#include <stdio.h>

using namespace std;

typedef void(*FuncPtr)();
typedef int(*FuncPtr2)();

void fun1()
{
}

int fun2()
{
    return 10;
}


int main(int argc, _TCHAR* argv[])
{
    FuncPtr fun[10];
    fun[0] = &fun1;

    //fun[1] = &fun2; //error C2440: “=”: 无法从“int (__cdecl *)(void)”转换为“FuncPtr”
    //fun[1] = static_cast<FuncPtr>(&fun2); //error C2440: “static_cast”: 无法从“int (__cdecl *)(int)”转换为“FuncPtr”

    fun[1] = reinterpret_cast<FuncPtr>(&fun2); //用强制转换将int fun 转为 void fun 保存起来


    FuncPtr2* pfun = reinterpret_cast<FuncPtr2*>(&fun[1]); //在需要使用的时候，再转换回来

    printf("run pfun = %d\n",(*pfun)()); //打印得到 "run pfun =10"

    system("pause");
    return 0;
}

C++ 类型转换

标签：c++   类型转换   

原文地址：http://blog.csdn.net/aizquan/article/details/38865709