c++的模板继承

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       作者：清林，博客名：飞空静渡

 

我们有这么一组这样的类，其类继承关系如下图：

我们先把base, man, 和woman的类写出来，test.h文件

#ifndef TEST_H #define TEST_H #include <iostream> using namespace std; class base { public: base (int id, bool bman):id_(id), bMan(bman){cout<<"base function!"<<endl;} virtual ~base (){} bool sexMan() { return bMan;} protected: int id_; bool bMan; // false is woman, true :is man }; class man :public base { public: man (int id):base(id, true){cout<<"I'am a man, id is "<<id_<<endl;} protected: }; class woman : public base { public: woman (int id): base(id, false){cout<<"I'am a woman, id is "<<id_<<endl;} protected: }; #endif

 

如果我们要写一个男教师的类manTeacher的话就得从man上继承，同理womanTeacher就得从woman上继承，这样我们就得写下两个类了，但这里我们可以通过模板来简化类的写，如下（在test.h文件下面添加）：

 

template<class T> class teacher : public T { public: teacher(int id):T(id){} void say() { if (sexMan()) cout<<"I'am a man teacher!"<<endl; else cout<<"I'am a woman teacher!"<<endl; } private: /* data */ };

 

我们测试一下，新建一个cpp文件，main.cpp

#include <vector> #include "test.h" int main(int argc, char *argv[]) { teacher<man> t1(5); t1.say(); }

 

在vc上可以直接编译，在g++上，要添加-fpermissive，添加这个可以让模板代码由出错降为警告，从而编译通过，vc可以直接编译通过。

编译：

g++ -g -Wall -fpermissive main.cpp

运行： ./a.out
base function!
I'am a man, id is 5
I'am a man teacher!

 

我们再次修改如下：

#include <vector> #include "test.h" int main(int argc, char *argv[]) { base* b = new teacher<man>(3); teacher<man> *t = (teacher<man> *)b; t->say(); return 0; }

 

编译输出：./a.out
base function!
I'am a man, id is 3
I'am a man teacher

 

再次修改main.cpp

#include <vector> #include "test.h" int main(int argc, char *argv[]) { std::vector<base*> vb; base* b1 = new teacher<man>(3); base* b2 = new teacher<woman>(5); vb.push_back(b1); vb.push_back(b2); for(std::vector<base*>::iterator it = vb.begin(); it != vb.end(); ++it) { if ((*it)->sexMan()) { teacher<man> *t = (teacher<man> *) (*it); t->say(); } else { teacher<woman> *t = (teacher<woman> *) (*it); t->say(); } } return 0; }

 

编译输出：./a.out
base function!
I'am a man, id is 3
base function!
I'am a woman, id is 5
I'am a man teacher!
I'am a woman teacher!