还在因为写项目函数太多而烦恼？C++模板一文带你解决难题

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📖专栏链接：c++

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💯文章目录

- - 💝一、什么是模板
  - 💖二、C++函数模板
  - 💓三、函数模板操作自定义类型
  - 💞四、C++类模板
  - 💕五、稍微复杂一点的类模板

💝一、什么是模板

模板是一种忽略数据的一种泛型编程。把数据当做未知量，当使用的时候传入类型的一种编程方式

语法

template <class T>//告诉编译器，接下来要用到一个未知类型是T类型
template <typename T>//等效class
template <class T1,class T2,class T3> //三个未知类型

#include<iostream>
#include<string>
using namespace std;
#if 0
int Max(int a, int b) 
{
	return a > b ? a : b;
}
float Max(float a, float b) 
{
	return a > b ? a : b;
}
double Max(double a, double b)
{
	return a > b ? a : b;
}
#endif
template <class T1> T1 Max(T1 a,T1 b)
{
	return a > b ? a : b;
}
int main() 
{
	cout << Max<int>(9, 10);
	return 0;
}

💖二、C++函数模板

函数模板调用
函数模板隐式调用
显示调用：函数名<未知类型>(函数参数)

函数模板本质就是函数传参
函数模板也是可以缺省

函数模板中存在变量
这种函数模板必须显示调用
变量传参只能传入常量

当函数模板和普通函数相遇
优先调用类型一致的普通函数
显示调用一定调用模板

函数模板重载
优先调用传参数目少的函数模板

#include<iostream>
#include<string>
using namespace std;
template <class T1> T1 Max(T1 a, T1 b) 
{
	return a > b ? a : b;
}
template <class _T1, class _T2, class _T3> void print(_T1 a, _T2 b, _T3 c) 
{
	cout << a << "\t" << b << "\t" << c << endl;
}
template <class _T1 = int, class _T2 = string, class _T3 = double> void printData(_T1 a, _T2 b, _T3 c)
{
	cout << a << endl << b << endl << c << endl;
}
template <class _T1,int size> _T1* createNew()
{
	_T1* createNew = new _T1[size];
	return createNew;
}
template <class _T1, int size=5> _T1* createParry()
{
	_T1* createNew = new _T1[size];
	return createNew;
}
template <class _Ty, int size = 4> void printArray2(_Ty array[])
{
	for (int i = 0; i < size; i++)
	{
		cout << array[i] << "\t";
	}
	cout << endl;
}
void Func1(int a, double b, string c) 
{
	cout << "普通函数" << endl;
}
template <class _T1, class _T2, class _T3> void Func1(_T1 a,_T2 b,_T3 c) { cout << "三个" << endl; }
template <class _T1, class _T2> void Func1(_T1 a, _T2 b, _T2 c) { cout << "两个" << endl; }
template <class _T1> void Func1(_T1 a,_T1 b,_T1 c) { cout << "一个" << endl; }

void test1() 
{
	//函数模板存在变量,必须显示调用
	int* parry = createNew<int, 5>();
	//变量缺省时候可以隐式调用
	double* king = createParry<double>();
	int p[4] = { 1,2,3,4 };
	printArray2(p);
}
void test2()
{
	//函数模板重载，普通函数
	Func1<int, double, string>(1,1.11,string("king"));
	Func1(1, 1.11,string("king"));
	Func1(1, string("asdd"),string("kkk"));
	Func1(1, 1, 1);
}
int main()
{
	//隐式调用
	cout << Max(1, 2) << endl;
	cout << Max(1.1, 1.2) << endl;
	cout << Max(string("abc"), string("abd")) << endl;
	print(123, string("king"), 1.55);

	//显示调用
	cout << Max<int>(1, 2) << endl;
	cout << Max<string>(string("abc"), string("abd")) << endl;
	print<string, int, double>("asdas", 123, 123.213);

	//函数模板的缺省
	printData(1, "dad", 1.11);
	printData<double, int, string>(1.11, 1, "dasdf");

	test1();
	test2();
	return 0;
}

💓三、函数模板操作自定义类型

操作自定义类型的关键点就是重载

#include<iostream>
#include<string>
using namespace std;
template <class _T1> void printpArry(_T1 arry[],int arryNums)
{
	for (int i = 0; i < arryNums; i++)
	{
		cout << arry[i] << endl;
	}
	cout << endl;
}
template <class _T1> void Sort(_T1 arry[], int arryNums) 
{
	for (int i = 0; i < arryNums; i++)
	{
		for (int j = 0; j < arryNums - i - 1; j++) 
		{
			if (arry[j] > arry[j + 1]) 
			{
				_T1 temp = arry[j];
				arry[j] = arry[j + 1];
				arry[j + 1] = temp;
			}
		}
	}
}
class MM 
{
public:
	MM(string name="", int age=0):name(name),age(age){}
	friend ostream& operator<<(ostream& out,const MM& object)
	{
		out << object.age << "\t" << object.name << endl;
		return out;
	}
	bool operator>(const MM& object) 
	{
		return this->name > object.name;
	}
	string Getname() const { return this->name; }
	int Getage() const { return this->age; }
protected:
	string name;
	int age;
};
template <class _T1> void Sort2(_T1 arry[], int arryNums,bool(*compare)(const _T1& one,const _T1& two))
{
	for (int i = 0; i < arryNums; i++)
	{
		for (int j = 0; j < arryNums - i - 1; j++)
		{
			if (compare(arry[j] , arry[j + 1]))
			{
				_T1 temp = arry[j];
				arry[j] = arry[j + 1];
				arry[j + 1] = temp;
			}
		}
	}
}
bool compareByname(const MM& one, const MM& two)
{
	return one.Getname() > two.Getname();
}
bool compareByage(const MM& one, const MM& two)
{
	return one.Getage() > two.Getage();
}
int main() 
{
	int parry[5] = { 1,20,6,7,90 };
	Sort(parry, 5);
	printpArry(parry, 5);
	MM mm[3];
	mm[0] = { "e",123 };
	mm[1] = { "b",241 };
	mm[2] = { "d",345 };
	Sort(mm, 3);
	printpArry(mm, 3);
	Sort2(mm, 3,compareByage);
	printpArry(mm, 3);
	return 0;
}

💞四、C++类模板

template修饰的类就是类模板
模板类必须显示实例化，简单来说必须要传参
模板类不是一个真正的类型
声明和实现必须写在一起，所谓一起就是同一个文件中
所有用到类型的地方必须要用类名<未知类型>的用法

类模板特化
局部特化：特殊化处理，例如两个未知变成一个未知类型
完全特化：具体化类型

#include<iostream>
#include<string>
using namespace std;
template <class _T1,class _T2> class Data
{
public:
	void print();
	static int count;
};
template <class _T1, class _T2> int Data<_T1, _T2>::count = 0;
template <class _T1, class _T2> void Data<_T1, _T2>::print() 
{
	cout << "类中模板函数" << endl;
}
//类模板的继承
template <class _T1, class _T2> class Son : public Data<_T1, _T2> 
{
public:
protected:
};
struct MMinfor 
{
	string name;
	int age;
};
ostream& operator<<(ostream& out, const MMinfor& object) 
{
	out << object.age << "\t" << object.name << endl;
	return out;
}
struct MMscore 
{
	int math;
	int english;
	int chinese;
};
ostream& operator<<(ostream& out, const MMscore& object)
{
	out << object.math << "\t" << object.english << "\t" << object.chinese << endl;
	return out;
}
template <class _T1, class _T2> class MM 
{
public:
	MM(_T1 one,_T2 two):one(one),two(two){}
	void print() { cout << one << "\t" << two << endl; }
protected:
	_T1 one;
	_T2 two;
};
void test1()
{
	MM < string, int > mm("king", 19);
	mm.print();
	MM<int, int> complaxe(1, 1);
	complaxe.print();
	//MMinfor info{string("zhang"), 18};
	//MMscore score{ 13,14,123 };
	//MM<MMinfor, MMscore> king(info, score);
	MM<MMinfor, MMscore> king({ "zhang",18 }, { 31,312,453 });
	king.print();
}
//类模板特化
template <class _T1, class _T2, class _T3> class A
{
public:
	A(_T1 one,_T2 two,_T3 three):one(one),two(two),three(three)
	{
		cout << "三个类型" << endl;
	}
protected:
	_T1 one;
	_T2 two;
	_T3 three;
};
//局部特化
template <class _T1> class A<_T1,_T1,_T1>
{
public:
	A(_T1 one, _T1 two, _T1 three) :one(one), two(two), three(three)
	{
		cout << "局部特化" << endl;
	}
protected:
	_T1 one;
	_T1 two;
	_T1 three;
};
//完全特化
template <> class A<int,int,int>
{
public:
	A(int one, int two, int three) :one(one), two(two), three(three)
	{
		cout << "完全特化" << endl;
	}
protected:
	int one;
	int two;
	int three;
};
void Test() 
{
	A<int, int, int> a(1, 2, 3);
	A<int, string, double> b(1, "as", 1.22);
	A<int, int, double> c(1, 2, 1.22);//三个类型
	A<string, string, string> d("qew", "fasd", "fads");
}
int main()
{
	Data<int, string> data;
	Data<string, int>* object = new Data<string, int>;
	data.print();
	object->print();
	//两个不同类型中的count,不会因为一个类型中值的改变而另一个类型中的值改变
	cout << Data<int, string>::count << endl;
	cout << Data<string, string>::count << endl;
	test1();
	Test();
	return 0;
}

💕五、稍微复杂一点的类模板

稍微复杂一点的模板就是模板类与模板类的嵌套，本质不难，大家学会剥洋葱，学会用别名替换即可

#include<iostream>
#include<string>
using namespace std;
template <class _T1, class _T2> class MM 
{
public:
	MM(_T1 one, _T2 two) :one(one), two(two) {}
	void print() { cout << one << "\t" << two << endl; }
	template <class _T1, class _T2> friend ostream& operator<<(ostream& out,const MM<_T1, _T2>& object);
protected:
	_T1 one;
	_T2 two;
};
template <class _T1, class _T2> ostream& operator<<(ostream& out,const MM<_T1, _T2>& object)
{
	out << object.one << "\t" << object.two << endl;
	return out;
}
template <class _T1, class _T2> class Data 
{
public:
	Data(_T1 one,_T2 two):one(one),two(two){}
	void print() { cout << one << "\t" << two << endl; }
	template <class _T1, class _T2>friend ostream& operator<<(ostream& out, const Data<_T1, _T2>& object);
protected:
	_T1 one;
	_T2 two;
};
template <class _T1, class _T2> ostream& operator<<(ostream& out, const Data<_T1, _T2>& object)
{
	out << object.one << "\t" << object.two << endl;
	return out;
}
int main() 
{
	MM<int, string> info(19, "king");
	MM<int, int> score(99, 88);
	Data< MM<int, string>, MM<int, int>> king(info, score);
	king.print();
	using kk = Data< MM<int, string>, MM<int, int>>;
	using kkk = MM<int, string>;
	Data<kk, kkk> data(king, info);
	data.print();

	return 0;
}