我们前面学习了函数模板、类模板了,我们现在有能力来开发一个数组类模板。但是还需要些知识点。
一、预备知识
1、模板参数可以是数值型参数
template
<typename T,int N>
void func
{
T a[N]; //使用模板参数定义局部数组
}
2、数值型参数的限制
- 变量不能作为模板参数
- 浮点数不能作为模板参数
- 类对象不能作为模板参数
本质:模板参数是在编译阶段处理的单元,因此,在编译阶段必须准确无误的唯一确定。
二、有趣的面试题
用你觉得最高效的办法求1+2+3.....+N的值!
#include <iostream>
#include <string>
using namespace std;
template
<typename T,int N>
void func()
{
T a[N] = {0};
for(int i = 0;i<N;i++)
{
a[i] = i;
}
for(int i = 0;i<N;i++)
{
cout << a[i] << endl;
}
}
template
< int N >
class Sum
{
public:
static const int VALUE = Sum<N-1>::VALUE + N;
};
template
< >
class Sum < 1 >
{
public:
static const int VALUE = 1;
};
int main()
{
cout << "1+2+3+...+10 = " << Sum<10>::VALUE << endl;
cout << "1+2+3+...+100 = " << Sum<100>::VALUE << endl;
return 0;
}
示例:数组模板类的实现
Array.h
#ifndef _ARRAY_H
#define _ARRAY_H
template
<typename T,int N>
class Array
{
T m_array[N];
public:
int length();
bool set(int index,T value);
bool get(int index,T& value);
T& operator[](int index);
T operator[] (int index) const;
virtual ~Array();
};
template
<typename T,int N>
int Array<T,N>::length()
{
return N;
}
template
<typename T,int N>
bool Array<T,N>::set(int index,T value)
{
bool ret = (0 <= index)&&(index < N);
if(ret)
{
m_array[index] = value;
}
return ret;
}
template
<typename T,int N>
bool Array<T,N>::get(int index,T& value)
{
bool ret = (0 <= index)&&(index < N);
if(ret)
{
value = m_array[index];
}
return ret;
}
template
<typename T,int N>
T& Array<T,N>::operator[](int index)
{
return m_array[index];
}
template
< typename T, int N >
T Array<T, N>::operator[] (int index) const
{
return m_array[index];
}
template
< typename T, int N >
Array<T, N>::~Array()
{
}
#endif
HeapArray.h
#ifndef _HEAPARRAY_H_
#define _HEAPARRAY_H_
template
< typename T >
class HeapArray
{
private:
int m_length;
T* m_pointer;
HeapArray(int len);
HeapArray(const HeapArray<T>& obj);
bool construct();
public:
static HeapArray<T>* NewInstance(int length);
int length();
bool get(int index, T& value);
bool set(int index ,T value);
T& operator [] (int index);
T operator [] (int index) const;
HeapArray<T>& self();
~HeapArray();
};
template
< typename T >
HeapArray<T>::HeapArray(int len)
{
m_length = len;
}
template
< typename T >
bool HeapArray<T>::construct()
{
m_pointer = new T[m_length];
return m_pointer != NULL;
}
template
< typename T >
HeapArray<T>* HeapArray<T>::NewInstance(int length)
{
HeapArray<T>* ret = new HeapArray<T>(length);
if( !(ret && ret->construct()) )
{
delete ret;
ret = 0;
}
return ret;
}
template
< typename T >
int HeapArray<T>::length()
{
return m_length;
}
template
< typename T >
bool HeapArray<T>::get(int index, T& value)
{
bool ret = (0 <= index) && (index < length());
if( ret )
{
value = m_pointer[index];
}
return ret;
}
template
< typename T >
bool HeapArray<T>::set(int index, T value)
{
bool ret = (0 <= index) && (index < length());
if( ret )
{
m_pointer[index] = value;
}
return ret;
}
template
< typename T >
T& HeapArray<T>::operator [] (int index)
{
return m_pointer[index];
}
template
< typename T >
T HeapArray<T>::operator [] (int index) const
{
return m_pointer[index];
}
template
< typename T >
HeapArray<T>& HeapArray<T>::self()
{
return *this;
}
template
< typename T >
HeapArray<T>::~HeapArray()
{
delete[]m_pointer;
}
#endif
#include <iostream>
#include <string>
#include "Array.h"
#include "HeapArray.h"
using namespace std;
int main()
{
Array<double, 5> ad;
for(int i=0; i<ad.length(); i++)
{
ad[i] = i * i;
}
for(int i=0; i<ad.length(); i++)
{
cout << ad[i] << endl;
}
cout << endl;
HeapArray<char>* pai = HeapArray<char>::NewInstance(10);
if( pai != NULL )
{
HeapArray<char>& ai = pai->self();
for(int i=0; i<ai.length(); i++)
{
ai[i] = i + 'a';
}
for(int i=0; i<ai.length(); i++)
{
cout << ai[i] << endl;
}
}
delete pai;
return 0;
}