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dynamic_cast, RTTI, 整理

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主要是参考下图,了解内存布局,然后写个实例程序就差不多明白了,但是需要熟悉指针转换。

1) 只有多态类才有RTTI信息,dynamic_cast正是运用RTTI进行转换,属于运行时类型检查。

2) dynamic_cast判断两个指针是否能转换时,用RTTI可以知道当前实际对象,然后遍历自己所有的父类,看是否有与目标类型一致的,如果有就可以进行转换。

3) dynamic_cast是安全的,可以通过检查返回值或异常捕捉来判断是否转成功。其中检查返回值用于指针转换,异常捕捉用于引用转换。

4) 补充一点,与static_cast不同,即使两个类没有直接继承关系,但是只要在一个类层次结构中,就有可能指向同一个对象,也就可以进行dynamic_cast。以下图为例,C继承自A,B。A, B指针就可以进行dynamic_cast,并可能成功。

    C * pc = new C;
    A* pa = pc;
    B* pb = pc;

    pb = dynamic_cast<B*>(pa); // 可以成功进行转换,因为二者指向的都是C对象。

 

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 下面的例子主要是关于RTTI的,打印出一个对象和她所有父类的运行时信息,这里的运行时信息主要是类的名字。

技术分享
#include "iostream"
#include "string" 
#include <typeinfo>
using namespace std;


class Zero
{
public:
    virtual void f111() { }
};

class Base : public Zero
{
public:
    virtual void f() { }
};

class Deri1234567890ve : public Base
{
};

typedef unsigned long DWORD;

struct PMD
{
    int mdisp;  //member displacement
    int pdisp;  //vbtable displacement
    int vdisp;  //displacement inside vbtable
};

struct RTTIBaseClassDescriptor
{
    struct TypeDescriptor* pTypeDescriptor; //type descriptor of the class
    DWORD numContainedBases; //number of nested classes following in the Base Class Array
    struct PMD where;        //pointer-to-member displacement info
    DWORD attributes;        //flags, usually 0
};


struct TypeDescriptor
{
    DWORD ptrToVTable;
    DWORD spare;
    char name[ ];
};

struct RTTIClassHierarchyDescriptor
{
    DWORD signature;      //always zero?
    DWORD attributes;     //bit 0 set = multiple inheritance, bit 1 set = virtual inheritance
    DWORD numBaseClasses; //number of classes in pBaseClassArray
    struct RTTIBaseClassArray* pBaseClassArray;
};

struct RTTICompleteObjectLocator

{

    DWORD signature; //always zero ?

    DWORD offset;    //offset of this vtable in the complete class

    DWORD cdOffset;  //constructor displacement offset

    struct TypeDescriptor* pTypeDescriptor; //TypeDescriptor of the complete class

    //int * ptr;
    struct RTTIClassHierarchyDescriptor* pClassDescriptor; //describes inheritance hierarchy

};




int main()
{
    /*Base *pderive = new Deri1234567890ve();
    int **ptr = (int **)(&pderive);
    int *ptable = (int *)(*(int *)(*ptr)); 
    int * rtti = ptable -1;

    RTTICompleteObjectLocator * RIIT_locator =   (RTTICompleteObjectLocator *)( *(int*)rtti);
    cout<<RIIT_locator->pTypeDescriptor->name<<endl;*/


    Base *pderive = new Deri1234567890ve();
    int *ptable = (int*)*(int*)pderive;
    int * rtti = ptable -1;

    // 显示当前类的名字“。。Deri1234567890ve。。”
RTTICompleteObjectLocator
* RIIT_locator = (RTTICompleteObjectLocator *)( *(int*)rtti); cout<<RIIT_locator->pTypeDescriptor->name<<endl; // 显示自己和所有父类的名字
int * p1 = (int*)(RIIT_locator->pClassDescriptor->pBaseClassArray); int * p2 = (int*)*(p1+2); TypeDescriptor* pDesc = (TypeDescriptor*)(*p2); cout<<"One of Base Classes: "<<pDesc->name<<endl; p1 = (int*)(RIIT_locator->pClassDescriptor->pBaseClassArray); p2 = (int*)*(p1 + 1); pDesc = (TypeDescriptor*)(*p2); cout<<"One of Base Classes: "<<pDesc->name<<endl; p1 = (int*)(RIIT_locator->pClassDescriptor->pBaseClassArray); p2 = (int*)*(p1); pDesc = (TypeDescriptor*)(*p2); cout<<"One of Base Classes: "<<pDesc->name<<endl; }
技术分享

 

参考:

浅议 Dynamic_cast 和 RTTI   http://www.cnblogs.com/zhyg6516/archive/2011/03/07/1971898.html

http://www.openrce.org/articles/full_view/23 

 

 

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dynamic_cast, RTTI, 整理

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原文地址:http://www.cnblogs.com/shouce/p/5544642.html

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