62.类模板
2023-04-18 15:54:44 时间
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;
};
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