62.类模板

1.类模板

1.1类模板基本概念

  函数模板，实际上是建立一个通用函数，其函数类型和形参类型不具体制定，用一个虚拟的类型来代表。这个通用函数就成为函数模板

●类模板用于实现类所需数据的类型参数化

template<class NameType, class AgeType>
class Person
{
public:
	Person(NameType name, AgeType age)
	{
		this->mName = name;
		this->mAge = age;
	}
	void showPerson()
	{
		cout << "name: " << this->mName << " age: " << this->mAge << endl;
	}
public:
	NameType mName;
	AgeType mAge;
};

void test01()
{
	//Person P1("德玛西亚",18); // 类模板不能进行类型自动推导 
	Person<string, int>P1("德玛西亚", 18);
	P1.showPerson();
}

1.2类模板做函数参数

//类模板
template<class NameType, class AgeType>
class Person{
public:
	Person(NameType name, AgeType age){
		this->mName = name;
		this->mAge = age;
	}
	void PrintPerson(){
		cout << "Name:" << this->mName << " Age:" << this->mAge << endl;
	}
public:
	NameType mName;
	AgeType mAge;
};

//类模板做函数参数
void DoBussiness(Person<string,int>& p){
	p.mAge += 20;
	p.mName += "_vip";
	p.PrintPerson();
}

int main(){

	Person<string, int> p("John", 30);
	DoBussiness(p);

	system("pause");
	return EXIT_SUCCESS;
}

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include<string>

//普通类继承类模版
template<class T>
class Father
{
public:
	Father()
	{
		m = 20;
	}
public:
	T m;
};

//普通类 继承 类模版
class Son :public Father<int>//要告诉编译器父类的泛型数据类型具体是什么类型
{
public:

};
//类模版 继承 类模版
template<class T1,class T2>
class Son2 :public Father<T2>//要告诉编译器父类的泛型数据类型具体是什么类型
{

};

void test()
{
	Son2<int,int> s;
	cout << s.m << endl;
}

int main()
{
	test();

	system("pause");
	return EXIT_SUCCESS;
}

3.类模板派生普通类

#pragma warning(disable:4996)
#define _CRT_SECURE_NO_WARNINGS 1

#include <iostream>
#include <string>
using namespace std;

//类模板
template<class T>
class MyClass {
public:
	MyClass(T property) {
		this->mProperty = property;
	}
public:
	T mProperty;
};

//子类实例化的时候需要具体化的父类，子类需要知道父类的具体类型是什么样的
//这样c++编译器才能知道给子类分配多少内存

//普通派生类
class SubClass : public MyClass<int> {
public:
	SubClass(int b) : MyClass<int>(20) {
		this->mB = b;
	}
public:
	int mB;
};

int main()
{
	SubClass son(1);
	cout << "son.mProperty:" << son.mProperty << "," << "son.mB:" << son.mB << endl;
    system("pause");
    return EXIT_SUCCESS;
}

输出：

son.mProperty:20,son.mB:1
请按任意键继续. . .

1.4模板派生类模板

//父类类模板
template<class T>
class Base
{
	T m;
};
template<class T >
class Child2 : public Base<double>  //继承类模板的时候，必须要确定基类的大小
{
public:
	T mParam;
};

void test02()
{
	Child2<int> d2;
}

1.5类模板类内实现

template<class NameType, class AgeType>
class Person
{
public:
	Person(NameType name, AgeType age)
	{
		this->mName = name;
		this->mAge = age;
	}
	void showPerson()
	{
		cout << "name: " << this->mName << " age: " << this->mAge << endl;
	}
public:
	NameType mName;
	AgeType mAge;
};

void test01()
{
	//Person P1("德玛西亚",18); // 类模板不能进行类型自动推导 
	Person<string, int>P1("德玛西亚", 18);
	P1.showPerson();
}

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include<string>

template<class NameType, class AgeType>
class Maker
{
public:
	Maker(NameType name, AgeType age);
	/*{
		this->name = name;
		this->age = age;
	}*/

	void printMaker();
	/*{
		cout << "Name:" << this->name << " Age:" << this->age << endl;
	}*/
public:
	NameType name;
	AgeType age;
};

//类模版的成员函数类外实现
//要写成函数模版
template<class NameType, class AgeType>
Maker<NameType, AgeType>::Maker(NameType name, AgeType age)
{

	cout << "构造函数" << endl;
	this->name = name;
	this->age = age;
}


template<class NameType, class AgeType>
void Maker<NameType, AgeType>::printMaker()
{
	cout << "Name:" << this->name << " Age:" << this->age << endl;
}

int main()
{
	Maker<string, int> m("haha", 20);
	m.printMaker();
	system("pause");
	return EXIT_SUCCESS;
}

1.6类模板类外实现

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<string>
using namespace std;

template<class T1, class T2>
class Person{
public:
	Person(T1 name, T2 age);
	void showPerson();

public:
	T1 mName;
	T2 mAge;
};


//类外实现
template<class T1, class T2>
Person<T1, T2>::Person(T1 name, T2 age){
	this->mName = name;
	this->mAge = age;
}


template<class T1, class T2>
void Person<T1, T2>::showPerson(){
	cout << "Name:" << this->mName << " Age:" << this->mAge << endl;
}

void test()
{
	Person<string, int> p("Obama", 20);
	p.showPerson();
}

int main(){

	test();

	system("pause");
	return EXIT_SUCCESS;
}

1.7类模板头文件和源文件分离问题

Person.hpp

#pragma once

template<class T1,class T2>
class Person{
public:
	Person(T1 name,T2 age);
	void ShowPerson();
public:
	T1 mName;
	T2 mAge;
};

template<class T1, class T2>
Person<T1, T2>::Person(T1 name, T2 age){
	this->mName = name;
	this->mAge = age;
}

template<class T1, class T2>
void Person<T1, T2>::ShowPerson(){
	cout << "Name:" << this->mName << " Age:" << this->mAge << endl;
}

main.cpp

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include<string>
#include"Person.hpp"

//模板二次编译
//编译器编译源码 逐个编译单元编译的

int main(){

	Person<string, int> p("Obama", 20);
	p.ShowPerson();


	system("pause");
	return EXIT_SUCCESS;
}

结论: 案例代码在qt编译器顺利通过编译并执行，但是在Linux和vs编辑器下如果只包含头文件，那么会报错链接错误，需要包含cpp文件，但是如果类模板中有友元类，那么编译失败！

解决方案: 类模板的声明和实现放到一个文件中，我们把这个文件命名为.hpp(这个是个约定的规则，并不是标准，必须这么写).

原因：

●类模板需要二次编译，在出现模板的地方编译一次，在调用模板的地方再次编译。

●C++编译规则为独立编译

1.8模板类碰到友元函数

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include <string>

template<class T1, class T2> class Person;
//告诉编译器这个函数模板是存在
template<class T1, class T2> void PrintPerson2(Person<T1, T2>& p);

//友元函数在类内实现
template<class T1, class T2>
class Person{
	//1. 友元函数在类内实现
	friend void PrintPerson(Person<T1, T2>& p){
		cout << "Name:" << p.mName << " Age:" << p.mAge << endl;
	}

	//2.友元函数类外实现
	//告诉编译器这个函数模板是存在
	friend void PrintPerson2<>(Person<T1, T2>& p);

	//3. 类模板碰到友元函数模板
	template<class U1, class U2>
	friend void PrintPerson(Person<U1, U2>& p);

public:
	Person(T1 name, T2 age){
		this->mName = name;
		this->mAge = age;
	}
	void showPerson(){
		cout << "Name:" << this->mName << " Age:" << this->mAge << endl;
	}
private:
	T1 mName;
	T2 mAge;
};

void test01()
{
	Person <string, int>p("Jerry", 20);
	PrintPerson(p);
}


// 类模板碰到友元函数
//友元函数类外实现  加上<>空参数列表，告诉编译去匹配函数模板
template<class T1 , class T2>
void PrintPerson2(Person<T1, T2>& p)
{
	cout << "Name2:" << p.mName << " Age2:" << p.mAge << endl;
}

void  test02()
{
	Person <string, int>p("Jerry", 20);
	PrintPerson2(p);   //不写可以编译通过，写了之后，会找PrintPerson2的普通函数调用，因为写了普通函数PrintPerson2的声明	
}

int main(){

	//test01();
	test02();
	system("pause");
	return EXIT_SUCCESS;
}

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include<string>


template<class NameType, class AgeType>
class Maker
{
	friend void printMaker(Maker<NameType, AgeType> &p)
	{
		cout << "类内实现" << p.name << " " << p.age << endl;
	}
public:
	Maker(NameType name, AgeType age)
	{
		this->name = name;
		this->age = age;
	}

	
private:
	NameType name;
	AgeType age;
};

void test01()
{
	Maker<string, int> m("悟空", 18);

	printMaker(m);
}

template<class NameType, class AgeType>
class Maker2;

//告诉编译器下面有printMaker2的实现
template<class NameType, class AgeType>
void printMaker2(Maker2<NameType, AgeType> &p);

template<class NameType, class AgeType>
class Maker2
{
	//1.在函数名和()之间加上<>。(使得可以去找函数模板)
	friend void printMaker2<>(Maker2<NameType, AgeType> &p);
	//2.编译器不知道printMaker2下面有没有实现，需要知道函数的结构
public:
	Maker2(NameType name, AgeType age)
	{
		this->name = name;
		this->age = age;
	}


private:
	NameType name;
	AgeType age;
};

//友元在类外实现要写成函数模版
template<class NameType, class AgeType>
void printMaker2(Maker2<NameType, AgeType> &p)
{
	cout << "类外实现的友元函数 " << p.name << " " << p.age << endl;
}

void test02()
{
	Maker2<string, int> m("贝吉塔", 18);

	printMaker2(m);
}

int main()
{
	
	test02();
	system("pause");
	return EXIT_SUCCESS;
}

2.类模板的应用

设计一个数组模板类(MyArray),完成对不同类型元素的管理

类模版实现数组.cpp

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
#include"MyArray.hpp"
#include<string>
class Maker
{
public:
	Maker(){}
	Maker(string name, int age)
	{
		this->name = name;
		this->age = age;
	}
public:
	string name;
	int age;
};

void printMaker(MyArray<Maker> &arr)
{
	for (int i = 0; i < arr.getSize(); i++)
	{
		cout << "姓名:" << arr[i].name << " 年龄:" << arr[i].age << endl;
	}
}
void test()
{
	MyArray<Maker> myarr(4);
	Maker m1("悟空", 18);
	Maker m2("贝吉塔", 30);
	Maker m3("短笛", 200);
	Maker m4("小林", 19);
	myarr.Push_Back(m1);
	myarr.Push_Back(m2);
	myarr.Push_Back(m3);
	myarr.Push_Back(m4);

	printMaker(myarr);

	MyArray<int> myint(10);
	for (int i = 0; i < 10; i++)
	{
		myint.Push_Back(i + 1);
	}

	for (int i = 0; i < 10; i++)
	{
		cout << myint[i] <<" ";
	}
	cout << endl;
}

int main()
{
	test();

	system("pause");
	return EXIT_SUCCESS;
}

MyArray.hpp

#pragma once

template<class T>
class MyArray
{
public:
	MyArray(int capacity)
	{
		this->mCapacity = capacity;
		this->mSize = 0;
		//T如果是Maker,这里要调用什么构造函数，要调用无参构造
		p = new T[this->mCapacity];

	}

	//拷贝构造
	MyArray(const MyArray &arr)
	{
		this->mCapacity = arr.mCapacity;
		this->mSize = arr.mSize;
		p = new T[arr.mCapacity];

		for (int i = 0; i < this->mSize; i++)
		{
			p[i] = arr.p[i];
		}
	}
	//赋值函数
	MyArray &operator=(const MyArray &arr)
	{
		if (this->p != NULL)
		{
			delete[] this->p;
			this->p = NULL;
		}

		p = new T[arr.mCapacity];
		this->mSize = arr.mSize;
		this->mCapacity = arr.mCapacity;
		for (int i = 0; i < this->mSize; i++)
		{
			p[i] = arr.p[i];

		}

		return *this;
	}

	//重载[]
	T &operator[](int index)
	{
		return this->p[index];
	}
	//尾插
	void Push_Back(const T &val)
	{
		if (this->mSize == this->mCapacity)
		{
			return;
		}

		this->p[this->mSize] = val;
		this->mSize++;
	}

	//尾删
	void Pop_Back()
	{
		if (this->mSize == 0)
		{
			return;
		}

		this->mSize--;
	}

	~MyArray()
	{
		if (this->p != NULL)
		{
			delete[] p;
			p = NULL;
		}
	}

	int getSize()
	{
		return this->mSize;
	}
private:
	T *p;
	int mCapacity;
	int mSize;
};