浅析C++中dynamic_cast和static_cast实例语法详解

static_cast< new_type >(expression)

double scores = 96.5;
int n = (int)scores;

double scores = 96.5;
int n = static_cast<int>(scores);

#include <iOStream>
#include <cstdlib>
using namespace std;
class Complex{
public:
    Complex(double real = 0.0, double imag = 0.0): m_real(real), m_imag(imag){ }
public:
    operator double() const { return m_real; }  //类型转换函数
private:
    double m_real;
    double m_imag;
};
int main(){
    //下面是正确的用法
    int m = 100;
    Complex c(12.5, 23.8);
    long n = static_cast<long>(m);  //宽转换，没有信息丢失
    char ch = static_cast<char>(m);  //窄转换，可能会丢失信息
    int *p1 = static_cast<int*>( malloc(10 * sizeof(int)) );  //将void指针转换为具体类型指针
    void *p2 = static_cast<void*>(p1);  //将具体类型指针，转换为void指针
    double real= static_cast<double>(c);  //调用类型转换函数
   
    //下面的用法是错误的
    float *p3 = static_cast<float*>(p1);  //不能在两个具体类型的指针之间进行转换
    p3 = static_cast<float*>(0X2DF9);  //不能将整数转换为指针类型
    return 0;
}

dynamic_cast <newType> (expression)

#include <iostream>
#include <iomanip>
using namespace std;
class Base{
public:
    Base(int a = 0): m_a(a){ }
    int get_a() const{ return m_a; }
    virtual void func() const { }
protected:
    int m_a;
};

class Derived: public Base{
public:
    Derived(int a = 0, int b = 0): Base(a), m_b(b){ }
    int get_b() const { return m_b; }
private:
    int m_b;
};

int main(){
    //情况①
    Derived *pd1 = new Derived(35, 78);
    Base *pb1 = dynamic_cast<Derived*>(pd1);
    cout<<"pd1 = "<<pd1<<", pb1 = "<<pb1<<endl;
    cout<<pb1->get_a()<<endl;
    pb1->func();
    //情况②
    int n = 100;
    Derived *pd2 = reinterpret_cast<Derived*>(&n);
    Base *pb2 = dynamic_cast<Base*>(pd2);
    cout<<"pd2 = "<<pd2<<", pb2 = "<<pb2<<endl;
    cout<<pb2->get_a()<<endl;  //输出一个垃圾值
    pb2->func();  //内存错误
    return 0;
}

#include <iostream>
using namespace std;
class A{
public:
    virtual void func() const { cout<<"Class A"<<endl; }
private:
    int m_a;
};
class B: public A{
public:
    virtual void func() const { cout<<"Class B"<<endl; }
private:
    int m_b;
};
class C: public B{
public:
    virtual void func() const { cout<<"Class C"<<endl; }
private:
    int m_c;
};
class D: public C{
public:
    virtual void func() const { cout<<"Class D"<<endl; }
private:
    int m_d;
};
int main(){
    A *pa = new A();
    B *pb;
    C *pc;
   
    //情况①
    pb = dynamic_cast<B*>(pa);  //向下转型失败
    if(pb == NULL){
        cout<<"Downcasting failed: A* to B*"<<endl;
    }else{
        cout<<"Downcasting successfully: A* to B*"<<endl;
        pb -> func();
    }
    pc = dynamic_cast<C*>(pa);  //向下转型失败
    if(pc == NULL){
        cout<<"Downcasting failed: A* to C*"<<endl;
    }else{
        cout<<"Downcasting successfully: A* to C*"<<endl;
        pc -> func();
    }
   
    cout<<"-------------------------"<<endl;
   
    //情况②
    pa = new D();  //向上转型都是允许的
    pb = dynamic_cast<B*>(pa);  //向下转型成功
    if(pb == NULL){
        cout<<"Downcasting failed: A* to B*"<<endl;
    }else{
        cout<<"Downcasting successfully: A* to B*"<<endl;
        pb -> func();
    }
    pc = dynamic_cast<C*>(pa);  //向下转型成功
    if(pc == NULL){
        cout<<"Downcasting failed: A* to C*"<<endl;
    }else{
        cout<<"Downcasting successfully: A* to C*"<<endl;
        pc -> func();
    }
   
    return 0;
}