【C++】 60_數組類模板

時間 2019-12-11

標籤 C++ 數組模板欄目 C&C++ 简体版

原文原文鏈接

預備知識

模板參數能夠是數值型參數（非類型參數）

template
< typename T, int N >
void func()
{
    T a[N];                  // 使用模板參數定義局部數組
}

func<double, 10>();

數值型模板參數的限制ios

變量不能做爲模板參數

浮點數不能做爲模板參數

類對象不能做爲模板參數

......

本質：
模板參數是在編譯階段被處理的單元，所以，在編譯階段必須準確無誤的惟一肯定。面試

有趣的面試題：
用你以爲最高效的方法求 1 + 2 + 3 + ... + N 的值！編程

編程實驗：數值類模板參數

#include <iostream>

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;    // 編譯器遞歸求值
};

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;
}

輸出:
1 + 2 + 3 + ... + 10 = 55
1 + 2 + 3 + ... + 100 = 5050

編程實驗：數組模板類

Array.h數組

#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 類可能被繼承，析構函數聲明爲虛函數
};

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 = (index >=0) && (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 = (index >=0) && (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

main.cpp數據結構

#include <iostream>
#include "Array.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;
    }
    
    return 0;
}

輸出：
0
1
4
9
16

編程實驗：堆數組模板類

HeapArray.h函數

#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<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(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 = (index >= 0) && (index < length());
    
    if( ret )
    {
        value = m_pointer[index];
    }
    
    return ret;
}

template
< typename T >
bool HeapArray<T>::set(int index, T value)
{
    bool ret = (index >= 0) && (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>:: operator = (const HeapArray<T>& obj)
{
    if( this != &obj )
    {
        T* pointer = new T[obj.m_length];
        
        if( pointer )
        {
            for(int i=0; i<obj.m_length; i++)
            {
                pointer[i] = obj.m_pointer[i];
            }
            
            m_length = obj.m_length;
            delete m_pointer;
            m_pointer = pointer;
        }    
    }
    return *this;
}

template
< typename T >
HeapArray<T>& HeapArray<T>::self()
{
    return *this;
}

template
< typename T >
HeapArray<T>::~HeapArray()
{
    delete[] m_pointer;
}

#endif

main.cppthis

#include <iostream>
#include "HeapArray.h"

using namespace std;

int main()
{
    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;
}