/* 用法:const_cast<type_id> (expression) 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。 一、常量指针被转化成非常量指针,并且仍然指向原来的对象; 二、常量引用被转换成非常量引用,并且仍然指向原来的对象; 三、常量对象被转换成非常量对象。 type_id 必须为指针或引用 */ class B { public: int m_iNum; B():m_iNum(50) {} }; void foo() { const B *b1 = new B(); //b1->m_iNum = 100; //compile error B *b2 = const_cast<B*>(b1); b2->m_iNum = 200; cout<<"b1: "<< b1->m_iNum <<endl; cout<<"b2: "<< b2->m_iNum <<endl; cout<<endl; const B b3; //b3.m_iNum = 100; //compile error B b4 = const_cast<B&>(b3);//b4 is another object b4.m_iNum = 200; cout<<"b3: "<<b3.m_iNum <<endl; cout<<"b4: "<<b4.m_iNum <<endl; cout<<endl; const B b5; //b5.m_iNum = 100; //compile error B &b6 = const_cast<B&>(b5); b6.m_iNum = 200; cout<<"b5: "<<b5.m_iNum <<endl; cout<<"b6: "<<b6.m_iNum <<endl; cout << endl; // force to convert const int x = 50; int* y = (int *)(&x);// same address, but the content is different *y = 200; cout << "x: "<<x<<" address: "<<&x<<endl; cout << "*y: "<<*y<<" address: "<<y<<endl; cout<<endl; // int const int xx = 50; int* yy = const_cast<int *> (&xx);// same address, but the content is different *yy = 200; cout << "xx: "<<xx<<" address: "<<&xx<<endl; cout << "*yy: "<<*yy<<" address: "<<yy<<endl; cout<<endl; // int const int xxx = 50; int yyy = const_cast<int&> (xxx);// another int yyy = 200; cout << "xxx: "<<xxx<<" address: "<<&xxx<<endl; cout << "yyy: "<<yyy<<" address: "<<&yyy<<endl; } int _tmain(int argc, char* argv[]) { foo(); return 0; }
result:
b1: 200
b2: 200
b3: 50
b4: 200
b5: 200
b6: 200
x: 50 address: 002CF880
*y: 200 address: 002CF880
xx: 50 address: 002CF884
*yy: 200 address: 002CF884
xxx: 50 address: 002CF88C
yyy: 200 address: 002CF888
可以改变const 自定义类的成员变量,但是对于内置数据类型,却表现未定义行为