预备知识

模板参数可以是数值型参数（非类型参数）

template< typename T, int N >void func(){    T a[N];                  // 使用模板参数定义局部数组}

func
    
     ();

数值型模板参数的限制

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被处理的单元，因此，在编译阶段必须准确无误的唯一确定。

有趣的面试题：

用你觉得最高效的方法求 1 + 2 + 3 + ... + N 的值！

编程实验：数值类模板参数

#include 
    
     using namespace std;template< typename T, int N >void func(){    T a[N] = {0};        for(int i=0; i
     
      class Sum{public:    static const int VALUE = Sum
      
       ::VALUE + N;    // 编译器递归求值};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;}

输出:1 + 2 + 3 + ... + 10 = 551 + 2 + 3 + ... + 100 = 5050

编程实验：数组模板类

Array.h

#ifndef _ARRAY_H_#define _ARRAY_H_template< typename T, int N >class Array{private:    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();                 // Array 类可能被继承，析构函数声明为虚函数};template< typename T, int N >int Array
    
     ::length(){    return N;}template< typename T, int N >bool Array
     
      ::set(int index, T value){    bool ret = (index >=0) && (index < N);        if( ret )    {        m_array[index] = value;    }        return ret;}template< typename T, int N >bool Array
      
       ::get(int index, T& value){    bool ret = (index >=0) && (index < N);        if( ret )    {        value = m_array[index];    }        return ret;}template< typename T, int N >T& Array
       
        ::operator[] (int index){    return m_array[index];}template< typename T, int N >T Array
        
         ::operator[] (int index) const{    return m_array[index];    }template< typename T, int N >Array
         
          ::~Array(){}#endif

main.cpp

#include 
    
     #include "Array.h"using namespace std;int main(){    Array
     
       ad;        for(int i=0; i

输出：014916

编程实验：堆数组模板类

HeapArray.h

#ifndef _HEAPRRAY_H_#define _HEAPARRAY_H_template< typename T >class HeapArray{private:    int m_length;    T* m_pointer;        HeapArray(int len);    HeapArray(const HeapArray& obj);    bool construct();public:    static HeapArray* 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& operator = (const HeapArray& obj);    HeapArray& self();    ~HeapArray();};template< typename T >HeapArray
    
     ::HeapArray(int len){    m_length = len;}template< typename T >bool HeapArray
     
      ::construct(){    m_pointer = new T[m_length];        return m_pointer != NULL;}template< typename T >HeapArray
      
       * HeapArray
       
        ::NewInstance(int length){    HeapArray
        
         * ret = new HeapArray(length);        if( !(ret && (ret->construct())) )    {        delete ret;        ret = 0;    }        return ret;}template< typename T >int HeapArray
         
          ::length(){ return m_length;}template< typename T >bool HeapArray
          
           ::get(int index, T& value){ bool ret = (index >= 0) && (index < length()); if( ret ) { value = m_pointer[index]; } return ret;}template< typename T >bool HeapArray
           
            ::set(int index, T value){ bool ret = (index >= 0) && (index < length()); if( ret ) { m_pointer[index] = value; } return ret;}template< typename T >T& HeapArray
            
             :: operator [] (int index){ return m_pointer[index];}template< typename T >T HeapArray
             
              :: operator [] (int index) const{ return m_pointer[index];}template< typename T >HeapArray
              
               & HeapArray
               
                :: operator = (const HeapArray
                
                 & obj){ if( this != &obj ) { T* pointer = new T[obj.m_length]; if( pointer ) { for(int i=0; i
                 
                  HeapArray
                  
                   & HeapArray
                   
                    ::self(){ return *this;}template< typename T >HeapArray
                    
                     ::~HeapArray(){ delete[] m_pointer;}#endif

main.cpp

#include 
    
     #include "HeapArray.h"using namespace std;int main(){    HeapArray
     
      * pai = HeapArray
      
       ::NewInstance(10);        if( pai != NULL )    {        HeapArray
       
        & ai = pai->self();                for(int i=0; i