12. C++模板

什么是模板

模板编程也可以叫做泛型编程，忽略数据类型的一种编程方式

//求最值问题 int  Max(int a,int b) { 	return a>b?a:b;     } double Max(int a,int b) { 	return a>b?a:b;         } string Max(string a,string b) { 	return a>b?a:b;         } //引入模板编程 template    //告诉编译器，下面会用到一个未知类型叫做type type Max(type a,type b) { 	return a>b?a:b;         } 

模板代码

#include  using namespace std; template   type Max(type a, type b)  { 	return a > b ? a : b; } //typename 可以用class 替换 template  void print(T data)  { 	cout << data << endl; }  int main()  { 	//隐式调用 	cout << Max(1, 2) << endl; 	cout << Max(1.1, 2.2) << endl; 	//string 和char* 有区别 	cout << Max(string("1ILoveyou"), string("2IMissyou")) << endl; 	//显示调用 <>传类型的参数 	cout << Max(1, 2) << endl;		//type=int  a=1 b=2 	cout << Max(string("1"), string("2")) << endl; 	cout << Max(1.2, 1.3) << endl; 	return 0; } 

函数模板

函数模板重载问题

• 函数模板和普通函数

• 函数模板和函数模板

#include  using namespace std; //No.1 模板与普通函数 int Max(int a, int b)  { 	cout << "普通函数..." << endl; 	return a > b ? a : b; } template  T Max(T a, T b)  { 	cout << "模板" << endl; 	return a > b ? a : b; } //No.2 模板与模板 template  void print(type1 one, type2 two, type3 three)  { 	cout << "三只" << endl; }  template 				//type1=int type2=double void print(type1 one, type1 two, type2 tow)     //int int double { 	cout << "两只" << endl; } template  void print(type one, type two, type three)  { 	cout << "一只" << endl; }   int main()  { 	cout << Max(1, 2) << endl;		//显式调用，百分百调用模板 	cout << Max(1, 2) << endl;			//优先调用类型确定的函数 	cout << "显示调用" << endl; 	print(1, 1.1, string("23")); 	print(1, 1, 1.22); 	print(1, 2, 3); 	cout << "隐式调用" << endl; 	print(1, 1, 2);						//需要传参越少先调用 	print(1, 1, string("sdsd"));		 	print(1, 1.11, string("sdsd"));		//只有一种选择 	return 0; } 

类成员函数是函数模板

//这种不叫做模板类型 class  MM  { public: 	template  	void print(T data)  	{ 		cout << data << endl; 	} protected:  }; int main() {     MM mm; 	mm.print(1); 	mm.print("string"); 	return 0;     } 

函数模板缺省

函数模板缺省和函数参数的缺省是一样的规则

//函数模板缺省 template  void printData(type1 one, type2 two)  { 	cout << one << endl; 	cout << two << endl; } int main() {      printData(1, 1.22); 	printData(1, string("dsfsdf"));     return 0; } 

函数模板传常量

//函数模板传常量 template  void printArray(T* array)  { 	for (int i = 0; i < size; i++)  	{ 		cout << array[i] << " "; 	} 	cout << endl; } int main() { 	int num[3] = { 1,2,3 }; 	printArray(num); 	//下面代码报错 	//int length = 3; 	//printArray(num); 	string str[4] = { "sdds","sd","sdsd" ,"sdds"}; 	printArray(str);     return 0; } 

类模板

类模板的基础

• 怎么写类模板

• 类模板不是一个完整类型，所以任何用到类名的地方都需要用类名<未知类型>的方式使用

• 怎么去使用类模板，类模板必须采用显式调用方式

• 类模板在多文件中不能分开写

• 可以写在.hpp文件中(声明和实现都在一起)

#include  #include 

类模板特化问题

• 局部特化
• 完全特化

特化的目的是为了适应不同数据的不同处理

#include  using namespace std; template  class Data { public: 	Data(_Ty1 one, _Ty2 two, _Ty3 three) :one(one), two(two), three(three) {} 	void printData() 	{ 		cout << (one + two + three) << endl; 	} private: 	_Ty1 one; 	_Ty2 two; 	_Ty3 three; };  //局部特化 //两个数据,打印两数之差 template  class Data<_Ty1,_Ty1,_Ty2>  { public: 	Data(_Ty1 one, _Ty2 two) :one(one), two(two){} 	void printData() 	{ 		cout << (one -two) << endl; 	} private: 	_Ty1 one; 	_Ty2 two; }; //只有一个数据,打印数据 template  class Data<_Ty1,_Ty1,_Ty1> { public: 	Data(_Ty1 one) :one(one){} 	void printData() 	{ 		cout << one << endl; 	} private: 	_Ty1 one; };  //完全特化 template <> class Data  { public: 	Data(string one,string two,string three):one(one),two(two),three(three) 	{  	} 	void printData(); private: 	string one; 	string two; 	string three; }; void Data::printData() { 	cout << one << " " << two << " " << three << endl; }  int main()  {  	Data data1(1); 	data1.printData(); 	Data data2(2, 1); 	data2.printData(); 	Data data3(1, 1.1, 1.2f); 	data3.printData(); 	Data data4("dsd","sdfd","sdfdsf"); 	data4.printData(); 	return 0; } 

模板操作自定义类型

模板操作自定义关键点在于重载

#include  #include  using namespace std;   class MM  { public: 	MM() = default; 	MM(string name, int age) :name(name), age(age) {} 	friend ostream& operator<<(ostream& out, const MM& object)  	{ 		out << object.name << " " << object.age; 		return out; 	} private: 	string name; 	int age; };  template  void printData(_Ty data) { 	cout << data << endl; }  template  class Data { public: 	//_Ty1=MM, _Ty2=int, _Ty3=int 	Data(_Ty1 one, _Ty2 two, _Ty3 three) :one(one), two(two), three(three) 	{  	} 	void printData()  	{ 		cout << one << " " << two << " " << three << endl; 	} private: 	_Ty1 one; 	_Ty2 two; 	_Ty3 three; };  int main() { 	printData(1); 	printData("string"); 	MM mm = { "小芳",18 }; 	printData(mm);  	Data data(MM("小芳",18),98,99); 	data.printData();  	Data mmData(MM("小芳", 18), MM("小芳", 18), MM("小芳", 18)); 	mmData.printData(); 	return 0; } 

模板嵌套模板

• 关键点在于大家自己要清楚类型如何表示（类型是由类名<类型>表示一个类型）

#include  using namespace std; template  class Data  { public: 	Data(_Ty1 one, _Ty2 two, _Ty3 three) :one(one), two(two), three(three) {} 	void printData()  	{ 		cout << one << " " << two << " " << three << endl; 	} 	friend ostream& operator<<(ostream& out, Data<_Ty1, _Ty2, _Ty3>& object) 	{ 		out << object.one << " " << object.two << " " << object.three; 		return out; 	} protected: 	_Ty1 one; 	_Ty2 two; 	_Ty3 three; };  template  class Info { public: 	Info(_Ty1 one, _Ty2 two) :one(one), two(two) {} 	void printData() 	{ 		cout << one << " " << two << endl; 	} 	//template   类中实现不需要修饰了，会出现重定义问题 	friend ostream& operator<<(ostream& out, Info<_Ty1, _Ty2>& object) 	{ 		out << object.one << " " << object.two << " "; 		return out; 	} protected: 	_Ty1 one; 	_Ty2 two;  }; template  class Student { public: 	Student(_Ty1 one) :one(one) {} 	void printData()  	{ 		cout << one << endl; 	} protected: 	_Ty1 one; };   int main()  { 	Data data(1,1,1);  //Data 	Info info(1, 2);		  //Info 	 	Info, Data> 		test1(Data(1, 1, 1), Data("ds", "sd", "sds")); 	//起别名 	using type1 = Data; 	using type2 = Data; 	//别名版本 	Infotest2(type1(1, 1, 1), type2("ds", "sd", "sds"));  	Data, Info, Info>  		test3(Info(1,"sd"), Info("sdds","dsds"),Info(1,1.11));  	test1.printData(); 	test2.printData(); 	test3.printData();  	Student, Info, Info>>  		stu(Data, Info, Info> 			(Info(1,1), Info(1,"sdsd"), Info("sds","sdsd")));  	stu.printData(); 	return 0; }