如果resize長度大于當(dāng)前容量時 : 則擴大分配新的內(nèi)存數(shù)組,并將舊數(shù)組拷貝至新數(shù)組及釋放舊數(shù)組.
如果resize長度小于當(dāng)前l(fā)ength時 : 則需要將多余的成員進行釋放,調(diào)用析構(gòu)函數(shù)實現(xiàn).
如果resize長度大于當(dāng)前l(fā)ength時 : 則需要調(diào)用默認構(gòu)造函數(shù)來填充內(nèi)部數(shù)組.

2.代碼實現(xiàn)

#ifndef VECTOR_H
#define VECTOR_H
#include "throw.h"
// throw.h里面定義了一個ThrowException拋異常的宏,如下所示:
//#include <iostream>
//using namespace std;
//#define ThrowException(errMsg)  {cout<<__FILE__<<" LINE"<<__LINE__<<": "<<errMsg<<endl; (throw errMsg);}
template <typename T>
class Vector
{
    T* m_data;
    int m_length;       // 有效數(shù)據(jù)的長度
    int m_capacity;     // 分配容量的長度
    // 分配
    T* allocate(int size)
    {
        T* arr = new T[size];
        if(arr == NULL) {
            ThrowException( "No memory to create DynamicArray object ...");
        }
        return arr;
    }
    // 重新分配
    void realloc(int capacity)
    {
        T* newData = allocate(capacity);
        for(int i=0; i<m_length; i++) {
            newData[i] = m_data[i];
        }
        delete[] m_data;
        m_data = newData;
        m_capacity = capacity;
    }
    // 調(diào)用析構(gòu)函數(shù)
    void destruct(int from, int end)
    {
        while(from++<end) {
           m_data[from].~T();
        }
    }
    // 調(diào)用默認構(gòu)造函數(shù)
    void defaultConstruct(int from, int end)
    {
        while(from++<end) {
           m_data[from] = T();
        }
    }
public:
    Vector(int lenght = 50)  { m_length = 0; m_data = allocate(lenght); m_capacity = lenght; }
    inline int capacity() const { return m_capacity; }     // 獲取容量
    inline int size()  { return m_length; }         // 獲取有效長度
    inline int length()  { return size(); }
    inline T *data() {  return m_data; }
    inline const T *data() const { return m_data; }
    inline bool isEmpty() const { return m_length == 0; }
    void clear()
    {
        if(!m_length) return;
        destruct(0, m_length);
        m_length = 0;
    }
    void resize(int asize)
    {
        if(asize == m_length) return;
        // 重新分配的大小>當(dāng)前容量時
        if(asize > m_capacity) {
            realloc(asize);
        }
        if (asize < m_length)    // 分配的大小<當(dāng)前大小時,則調(diào)用析構(gòu)
            destruct(asize, m_length);
        else        // 分配的大小>當(dāng)前大小時,則調(diào)用默認構(gòu)造
            defaultConstruct(m_length, asize);
        m_length = asize;
    }
    // 尾部追加一個元素
    void append(const T &t)
    {
        if(m_length == m_capacity) {
            realloc(m_capacity+20);     // 如果容量滿了,則默認增加20個容量.方便后面append無需再次分配內(nèi)存
        }
        m_data[m_length] = t;
        m_length++;
    }
    T& operator[] (int i)
    {
        if((0 <= i) && (i < length()))
        {
            return m_data[i];
        }
        else
        {
            ThrowException("Parameter i is invalid ...");
        }
    }
    T operator[] (int i) const
    {
        return m_data[i];
    }
};
#endif // VECTOR_H

3.測試運行

測試如下所示:

class Test {
public:
    int number;
    Test(int n = 0) {
        number = n;
    }
};
int main(int argc, char *argv[])
{
   Vector<Test> arr;
   for(int i = 0; i < 10; i++)
       arr.append(Test(i));
   cout<<"********* Arr Len:"<<arr.length()<<" capacity:"<<arr.capacity()<<endl;
   for(int i = 0; i < arr.length(); i++)
       cout<<"arr []:"<<arr[i].number<<endl;
   cout<<"*********"<<endl;
   arr.resize(13);
   cout<<"********* Arr Len:"<<arr.length()<<" capacity:"<<arr.capacity()<<endl;
   for(int i = 0; i < arr.length(); i++)
       cout<<"arr []:"<<arr[i].number<<endl;
   cout<<"*********"<<endl;
   arr.resize(5);
   cout<<"********* Arr Len:"<<arr.length()<<" capacity:"<<arr.capacity()<<endl;
   for(int i = 0; i < arr.length(); i++)
       cout<<"arr []:"<<arr[i].number<<endl;
   cout<<"*********"<<endl;
    return 0;
}

運行如下所示: