dynamic_cast C + +

Let's take a look at the four major conversions that others summarize

Static_cast, dynamic_cast, Const_cast, reinterpret_cast

http://www.jellythink.com/archives/205

To add to this,

1.dynamic_cast the parent class must contain a virtual function when making a downstream conversion (essentially, a virtual function table must be included)

There is no problem with the upstream conversion (whether it is a virtual function or not), whether it is a pointer or a reference, it will have this restriction

This feature is mentioned in the above link but only said that in the void* conversion requires a virtual function, not comprehensive;

See the code below

1 classParent {2 3  Public :4      voidfoo () {5     6cout <<"This is the Parent ' s foo function"<<Endl;7     }8 9 };Ten classChilda: PublicParent { One  A  -  - }; the  - classCHILDB: PublicParent { -  -  +  - }; +  Atypedefvoid(*fun) (void); at  - intMainintargcChar**AGR) - { -Parent * pp =NewParent (); -  -childa* PA = dynamic_cast<childa*>(PP); in  　　 
/*Parent pp;
parent& pRea = pp;
childa& pa = dynamic_cast<childa&> (PRea);
*/
To report the same mistake
 -     return 0; to}

Because there is no virtual function in the base class parent, the error is directly in line 28, and the compilation is not possible.

The error is: the operand of the run-time dynamic_cast must contain the Polymorphic class type;

2.dynamic_cast can reference the type of conversion, but for the downstream conversion, compile without error, run times wrong

See the following code, (contains the same base class, cross-class conversions)

1 //Test.cpp: Defines the entry point of the console application. 2 //3 4#include"stdafx.h"5#include <iostream>6 using namespacestd;7 classParent {8 9  Public :Ten     Virtual voidfoo () { One      Acout <<"This is the Parent ' s foo function"<<Endl; -     } -  the }; -  -  - classChilda: PublicParent { +  -  +  A }; at  - classCHILDB: PublicParent { -  -  -  - }; in  -typedefvoid(*fun) (void); to  + intMainintargcChar**AGR) - { the Parent pp; *parent& PRea =pp; $childa& PA = dynamic_cast<childa&>(PRea);Panax Notoginseng     /* - Childb pp; the childb& pRea = pp; + childa& pa = dynamic_cast<childa&> (pRea); A     */ the      +  -  $  $     return 0; -}

Error is: Std::bad_cast, run times wrong

But the cross-class conversions for the same base class

The pointer is not an error, just get the empty

//Test.cpp: Defines the entry point of the console application. //#include"stdafx.h"#include<iostream>using namespacestd;classParent { Public :    Virtual voidfoo () {cout<<"This is the Parent ' s foo function"<<Endl; }};classChilda: PublicParent {};classCHILDB: PublicParent {};typedefvoid(*fun) (void);intMainintargcChar**AGR) {Childb* pp =NewChildb; Childa* PA = dynamic_cast<childa*>(PP); ///the PA here is null, but not an error .    return 0;} 

dynamic_cast C + +