std::dynamic_pointer_cast

Code Cpp

http://www.cplusplus.com/reference/memory/dynamic_pointer_cast/
这个demo是用dynamic_pointer_cast 来确保（派生-->基类）转换是OK的

下面是(派生-->基类)的逻辑
http://www.cnblogs.com/ider/archive/2011/08/01/cpp_cast_operator_part5.html

• 虚函数是dynamic_cast转换能够进行的前提条件

#include <stdio.h>
#include <memory>
#include <string>
#include <iostream>
//class AA {
//public:
//    //This makes CGpuResultBase a polymorphic type
//    virtual ~AA(){}
//public:
//    static int type; 
//};
//
//class BB : public AA {
//public:
//    int index; 
//};
//
//int AA::type = 4;
struct AA {
    static int type;  
    //This makes CGpuResultBase a polymorphic type
    virtual ~AA(){}
};
struct BB :  AA {
    static int index; 
    BB() {
        type = index;
    }
};
int AA::type = 1;
int BB::index = 2;
int fun(std::shared_ptr<AA> &p)
{
    std::shared_ptr<BB> b(new BB());
    b->type = 1;
    std::cout <<"b:"<< b << std::endl;
    b->index = 3;
    p = std::dynamic_pointer_cast<AA>(b);
}
int main(int argc, char **argv)
{
    std::shared_ptr<AA> p;
    std::shared_ptr<BB> b;
    std::cout <<"P:" << p << std::endl;
    fun(p);
    //std::cout <<"P:" << p << std::endl;
    std::cout << p->type << std::endl;
    b = std::dynamic_pointer_cast<BB> (p); //not safe but right
    std::cout << b->type << std::endl;
    std::cout << b->index << std::endl;
}

各种cast

const_cast <new_type> (expression)  //移除 const跟volatile 属性
static_cast <new_type> (expression) //不安全的类型装换
reinterpret_cast <new_type> (expression)//指针跟整数互转
dynamic_cast <new_type> (expression)//基类 派生类互转 基类必须有虚函数