11-3 測試 Vec 類別

目前我們的 Vec 類別如下：
[vec.h]
#ifndef VEC_H_INCLUDED
#define VEC_H_INCLUDED

class Vec {
private:
 int *m_data;
 int m_size;
 int m_capacity;
public:
 Vec();
 ~Vec();
 int size();
 int capacity();
 void push_back(int val);
 void pop_back();
};

Vec::Vec()
{
 m_data = nullptr;
 m_size = 0;
 m_capacity = 0;
}

Vec::~Vec()
{
 if(m_data!=nullptr)
 {
 delete [] m_data;
 }
}

int Vec::size()
{
 return m_size;
}

int Vec::capacity()
{
 return m_capacity;
}

void Vec::push_back(int val)
{
 // 如果空間不夠用
 if(m_size==m_capacity)
 {
 // 每次成長為原來的 2 倍大小
 int new_capacity = m_capacity*2;

 if(new_capacity==0)
 new_capacity = 1;

 // 配置一塊新的空間
 int *new_data = new int[new_capacity];
 // 把資料搬到新的空間
 for(int i=0; i<m_size; i++)
 {
 new_data[i] = m_data[i];
 }
 // 釋放舊的空間，改用新空間
 if(m_data!=nullptr)
 delete [] m_data;

 m_data = new_data;
 m_capacity = new_capacity;
 }

 m_data[m_size] = val;
 m_size++;
}

void Vec::pop_back()
{
 m_size--;
}

#endif // VEC_H_INCLUDED

在主程式中引入其標頭檔來使用看看。
#include <iostream>
#include "vec.h"

using namespace std;

int main()
{
 Vec a;

 a.push_back(1);
 cout << "Cap:" << a.capacity() << " Size:" << a.size() << endl;
 a.push_back(3);
 cout << "Cap:" << a.capacity() << " Size:" << a.size() << endl;
 a.push_back(5);
 cout << "Cap:" << a.capacity() << " Size:" << a.size() << endl;
 a.push_back(7);
 cout << "Cap:" << a.capacity() << " Size:" << a.size() << endl;
 a.push_back(9);
 cout << "Cap:" << a.capacity() << " Size:" << a.size() << endl;

 return 0;
}

注意看 capacity 和 size 的變化。

Cap:1 Size:1
Cap:2 Size:2
Cap:4 Size:3
Cap:4 Size:4
Cap:8 Size:5