c++超基础：函数模版

一、泛指编程

template<typename T> 告诉编译器使用函数模版，T表示泛指的类型，废话不多说，直接实践

二、示例

#include <iostream>
#include <cstring>

using namespace std;

#define GetArrayLen(array, len) (len = sizeof(array)/sizeof(array[0]))

template<typename T>

void Swap(T &a, T &b)
{
	T t = a;
	a = b;
	b = t;
}


template<typename T>

void SelectSort(T *array, int length)
{
	int min_index;
	for (int i=0; i<length-1; i++)
	{
		min_index = i;
		for (int j=i+1; j<length; j++)
		{
			if (array[j] < array[min_index])
			{
				min_index = j;
			}
		}	
		if (min_index != i)
		{
			Swap(array[min_index], array[i]);
		}
	}
}

template<typename T>

void BubbleSort(T *array, int length)
{
	int min_index;
	for (int i=0; i<length-1; i++)
	{
		for (int j=i+1; j<length; j++)
		{
			if (array[j] < array[i])
			{
				Swap(array[j], array[i]);
			}
		}
	}
}

template<typename T>

void Print(T *array, int length)
{
	for (int i = 0; i<length; i++)
	{
		cout<<array[i]<<endl;
	}
}

int main()
{
	int a = 1;
	int b = 2;

	Swap(a, b);
	cout<<"a: "<<a <<" "<<"b: "<<b <<endl;
	float fa = 1.1;
	float fb = 2.2;

	Swap(fa, fb);
	cout<<"fa: "<<fa <<" "<<"fb: "<<fb <<endl;

	char *str1 = "Hello";
	char *str2 = "World";
	Swap(str1, str2);
	cout<<str1<<" "<<str2<<endl;

	int array[] = {4,5,2,1,3,6,7,9,};
	
	int len = 0;
	GetArrayLen(array, len);
	SelectSort<int>(array, len);
	Print<int>(array, len);

	BubbleSort<int>(array, len);
	Print<int>(array, len);

	return 0;
}

三、函数重载与模版

1、C++编译器会优先考虑普通函数

2、如果函数模版可以产生一个更好的匹配，那么会选择模版

3、可以通过空模版实参列表的语法限定编译器只通过模版来匹配函数

Note:

*普通函数会自动进行类型转换

*函数模版不会进行自动类型转换

#include <iostream>
#include <cstring>

using namespace std;

template<typename T>

T Max(T a, T b)
{
	cout<< "T Max(T a, T b)"<<endl;
	return a > b ? a : b;
}

int Max(int a, int b)
{
	cout<< "int Max(int a, int b)"<<endl;
	return a > b ? a : b;
}

template<typename T>

T Max(T a, T b, T c)
{
	cout<< "T Max(T a, T b, T c)"<<endl;
	return Max(Max(a, b), c);
}

template<typename RT, typename T1, typename T2>

RT Add(T1 a, T2 b)
{
	cout<< "RT Add(T1 a, T2 b)"<<endl;
	return static_cast<RT>(a + b);
}

int main()
{
	int a = 1;
	int b = 2;
	int c = 3;

	cout<<Max(a, b)<<endl;
	cout<<Max<>(a, b)<<endl;
	
	cout<<Max(1.1, 2.2)<<endl;
	cout<<Max(a, b, c)<<endl;

	cout<<Max('a', 100)<<endl;//必然调用普通函数，字符'a'将被打印为其对应的整形（ASCII码）
							//多参数模版提供了解决方案，注意把返回值类型写在第一位
	cout<<Add<double, double, double>('a', 3.3)<<endl;//等价于下一句
	cout<<Add<double>('a', 3.3)<<endl;

	return 0;
}