c++ template笔记

1. 数组

 

template <typename T, int N>
void array_print(T (&arr)[N])
{
	for(int i = 0; i < N; ++i)
	{
		cout << arr[i] << endl;
	}
}

 

int arr[5] = {1, 2, 3, 4, 5};
	array_print(arr); //实例成 array_print(int(&)[5])

 

2. 返回值

 

template <class T1, class T2, class T3>
T1 sum(T2 x, T3 y)
{
	return x.size() + y.size();
}

 

size_t l = sum<size_t>(string("xx"), string("yyy"));

3. 非类型形参数

 

 

template<int w, int h>
int area()
{
	return w * h;
}

 

int a = area<8,6>();

4. 特化

 

 

template <typename T>
int compare(const T &v1, const T &v2)
{
	if(v1 < v2) return -1;
	if(v2 < v1) return 1;
	return 0;
}

template <>
int compare<const char*>(const char* const &v1, const char* const &v2)
{
	return strcmp(v1, v2);
}

 

const char *str1 = "hello", *str2 = "world";
	int n1 = 1, n2 = 2;
	compare(str1, str2);
	compare(n1, n2);

5.  缺省模板参数

 

 

template <typename T1, typename T2 = bool>
class A {
public:
	A() : m_value1(), m_value2()
	{
	}
	~A()
	{

	}
private:
	T1 m_value1;
	T2 m_value2;
};

 

A<int> aa;

6. traits

 

 

template <typename T>
class TypeTraits;

template <>
class TypeTraits<char>{
public:
	typedef int ReturnType;
};

template <>
class TypeTraits<short>{
public:
	typedef int ReturnType;
};

template <>
class TypeTraits<int>{
public:
	typedef int ReturnType;
};

template <>
class TypeTraits<float>{
public:
	typedef double ReturnType;
};

template <typename T,typename Traits>
typename Traits::ReturnType average(T const* begin, T const* end)
{
	typedef typename Traits::ReturnType ReturnType;
	ReturnType total = ReturnType();
	int count = 0;
	while (begin != end){
		total += * begin;
		++begin;
		++count;
	}
	return total / count;
}

 

char str[] = "i love you";
	cout << average<char,TypeTraits<char> >(&str[0],&str[10]) << endl; // 看class TypeTraits<char>

参考文献：

 

1. <<C++ Primer>>

2. http://www.cnblogs.com/stephen-liu74/archive/2012/09/12/2639736.html

3. http://www.cppblog.com/youxia/archive/2008/08/30/60443.html