C++：RTTI(RunTime Type Information)運行時類型資訊 詳解

RTTI, RunTime Type Information, 運行時類型資訊, 是多態的主要組成部分,

通過運行時(runtime)確定使用的類型, 執行不同的函數,複用(reuse)介面.

dynamic_cast<>可以 使基類指標轉換為衍生類別的指標, 通過判斷指標的類型, 可以決定使用的函數.

typeid(), 可以判斷類型資訊, 判斷指標指向位置, 在多態中, 可以判斷基類還是衍生類別.

代碼:

/*  * test.cpp  *  *  Created on: 2014.04.22  *      Author: Spike  */      /*eclipse cdt, gcc 4.8.1*/      #include <iostream>  #include <typeinfo>              using namespace std;        class Base {  public:      virtual void fcnA() {          std::cout << "base" << std::endl;      }  };        class Derived : public Base {  public:      virtual void fcnB() {          std::cout << "derived" << std::endl;      }  };        void fcnC(Base* p) {      Derived* dp = dynamic_cast<Derived*>(p);      if (dp != NULL)          dp->fcnB();      else        p->fcnA();  }        void fcnD(Base* p) {      if (typeid(*p) == typeid(Derived)) {          Derived* dp = dynamic_cast<Derived*>(p);          dp->fcnB();      } else        p->fcnA();  }        int main(void) {      Base* cp = new Derived;      std::cout << typeid(cp).name() << std::endl;      std::cout << typeid(*cp).name() << std::endl;      std::cout << typeid(&(*cp)).name() << std::endl;      fcnC(cp);      fcnD(cp);      Base* dp = new Base;      fcnC(dp);      fcnD(dp);            return 0;  }

輸出:

P4Base  7Derived  P4Base  derived  derived  base  base

以上代碼只是樣本,

更多精彩內容：http://www.bianceng.cnhttp://www.bianceng.cn/Programming/cplus/

具體使用時, 避免使用dynamic_cast<>和typeid()去判斷類型, 直接通過多態即可.

注意多態的綁定只能通過指標, 如fcnC(Base*), 或引用, 如fcnD(Base&), 實現動態綁定, 兩者效果相同;

都會根據輸入的類型,動態綁定虛函數(virtual function).

代碼如下:

/*  * test.cpp  *  *  Created on: 2014.04.22  *      Author: Spike  */      /*eclipse cdt, gcc 4.8.1*/      #include <iostream>  #include <typeinfo>              using namespace std;        class Base {  public:      virtual void fcn() {          std::cout << "base" << std::endl;      }  };        class Derived : public Base {  public:      virtual void fcn() override {          std::cout << "derived" << std::endl;      }  };        void fcnC(Base* p) {      p->fcn();  }        void fcnD(Base& p) {      p.fcn();  }        int main(void) {      Base* cp = new Derived;      std::cout << typeid(cp).name() << std::endl;      std::cout << typeid(*cp).name() << std::endl;      fcnC(cp);      fcnD(*cp);      Base* dp = new Base;      fcnC(dp);      fcnD(*dp);            Base& cr = *cp;      std::cout << typeid(&cr).name() << std::endl;      std::cout << typeid(cr).name() << std::endl;      fcnC(&cr);      fcnD(cr);      Base& dr = *dp;      fcnC(&dr);      fcnD(dr);            return 0;  }

輸出:

P4Base  7Derived  derived  derived  base  base  P4Base  7Derived  derived  derived  base  base

作者：csdn部落格 Spike_King