C++详解如何实现动态数组

动态数组

动态数组Vector可以动态扩展内存，其采用连续的内存空间，当内存空间不足，便以原来的容量的2倍或者1.5倍成倍的扩展，将原有的数组元素拷贝到新分配的内存空间中，释放原有的内存空间，新的元素将存入的新分配的内存空间。

示例代码

动态数组vector的size函数和capacity函数，分别作为求数组中现有的元素的个数和数组所能容纳的元素的个数。下面直接上实现的代码。

DynamicArray .h

#pragma once
class DynamicArray {
public:
	DynamicArray();
	~DynamicArray();
	void push_back_Array(int value);
	void insertValueByPosArray(size_t pos,int value);
	void removeByValueFromArray(int value);
	void removeByPosFromArray(size_t pos);
	int findPosByValueArray(int value);
	int findValueByPosArray(size_t pos);
	void reclaimSpaceArray();
	void clearArray();
	int getCapacity();
	int getCount();
	void printArray();
private:
	int *m_pArr;
	size_t m_size;
	size_t m_capacity;
};

DynamicArray .cpp

#include "DynamicArray.h"
#include <iostream>
using namespace std;
// DynamicArray.cpp 
DynamicArray::DynamicArray()
{
	m_size = 0;
	m_capacity = 20;
	m_pArr = new int[m_capacity];
	if (m_pArr == nullptr)
	{
		cout << "new 开辟空间失败" << endl;
	}
}
DynamicArray::~DynamicArray()
{
	if (m_pArr != nullptr) 
	{
		delete[] m_pArr;
		m_pArr = nullptr;
	}
	m_size = 0;
	m_capacity = 0;
}
void DynamicArray::push_back_Array(int value)//push_back
{
	if (m_pArr == nullptr)
	{
		return;
	}
	reclaimSpaceArray();
	m_pArr[m_size] = value;
	m_size++;
}
void DynamicArray::insertValueByPosArray(size_t pos, int value)//插入insert(可以在前，中，后插入)
{
	if (m_pArr == nullptr)
	{
		return;
	}
	reclaimSpaceArray();
	for (size_t i = m_size - 1; i >= pos; --i)//pos为下标的数，从0开始
	{
		m_pArr[i + 1] = m_pArr[i];
	}
	m_pArr[pos] = value;
	m_size++;
}
void DynamicArray::removeByValueFromArray(int value)
{
	if (m_pArr == nullptr)
	{
		return;
	}
	int nPos = findPosByValueArray(value);
	removeByPosFromArray(nPos);
}
void DynamicArray::removeByPosFromArray(size_t pos)//pos为下标的数，从0开始
{
	if (m_pArr == nullptr)
	{
		return ;
	}
	if (pos < 0 || pos >= m_size)//pos的最大值为m_size-1
	{
		return ;
	}
	//找到被删除位置的下一位
	for (size_t i = pos + 1; i < m_size; ++i)
	{
		m_pArr[i - 1] = m_pArr[i];
	}
	m_size--;
}
int DynamicArray::findPosByValueArray(int value)
{
	size_t nPos = -1;
	if (m_pArr == nullptr)
	{
		return nPos;
	}
	for (size_t i = 0; i < m_size; ++i)
	{
		if (m_pArr[i] == value)
		{
			nPos = i;
			break;
		}
	}
	return nPos;
}
int DynamicArray::findValueByPosArray(size_t pos)
{
	if (m_pArr == nullptr)
	{
		return -1;
	}
	if (pos < 0 || pos >= m_size)
	{
		return -1;
	}
	return m_pArr[pos];
}
void DynamicArray::reclaimSpaceArray()
{
	if (m_size == m_capacity)
	{
		int *newArr = new int[m_capacity * 2];
		if (newArr == nullptr)
		{
			cout << "new 开辟空间失败" << endl;
			return;
		}
		memset(newArr, 0, m_capacity * 2 * sizeof(int));//第三个参数为字节数
		memcpy(newArr, m_pArr, m_size * sizeof(int));//第三个参数为字节数
		//下面这种逐个赋值的方式也可以使用
		//for (size_t i = 0; i < m_capacity; i++)
		//{
		//	newArr[i] = m_pArr[i];
		//}
		m_capacity = m_capacity * 2;
		if (m_pArr) {
			delete[] m_pArr;
			m_pArr = nullptr;
		}
		m_pArr = newArr;
	}
}
void DynamicArray::clearArray()//vector中clear()只是改变size的大小
{
	m_size = 0;
}
int DynamicArray::getCapacity()
{
	return m_capacity;
}
int DynamicArray::getCount()
{
	return m_size;
}
void DynamicArray::printArray()
{
	for (size_t i = 0; i < m_size; ++i)
	{
		//下面两种方式打印都可以
		cout << m_pArr[i] << " ";
		//int ret = findValueByPosArray(i);
		//cout<< ret<< " ";
	}
	cout << endl;
}

main.cpp

#include <iostream>
#include "DynamicArray.h"
using namespace std;
void test() {
	DynamicArray * pArray = new DynamicArray;
	int i = 0;
	while (i++ < 11) 
	{
		pArray->push_back_Array(i);
	}
	pArray->printArray();
	cout <<"size= "<< pArray->getCount() << endl;
	cout << "容量： " << pArray->getCapacity() << endl;
	pArray->insertValueByPosArray(5,12);
	pArray->printArray();
	cout << "insert after size= " << pArray->getCount() << endl;
	cout << "insert after 容量： " << pArray->getCapacity() << endl;
	pArray->removeByValueFromArray(2);
	pArray->printArray();
	cout << "remove after size= " << pArray->getCount() << endl;
	cout << "remove after 容量： " << pArray->getCapacity() << endl;
	pArray->removeByPosFromArray(3);
	pArray->printArray();
	cout << "remove by pos after size= " << pArray->getCount() << endl;
	cout << "remove by pos after 容量： " << pArray->getCapacity() << endl;
	cout<<"find 2 of pos: "<<pArray->findPosByValueArray(2)<<endl;
	cout << "find 8 of pos: " << pArray->findPosByValueArray(8) << endl;
	cout << "value at pos of 6: " << pArray->findValueByPosArray(6) << endl;
	pArray->clearArray();
	cout << "size= " << pArray->getCount() << endl;
	cout << "容量： " << pArray->getCapacity() << endl;
	if (pArray)
	{
		delete pArray;
		pArray = nullptr;
	}
}
int main()
{
	test();
	return 0;
}

运行环境

以上代码的运行环境为：vs2017控制台输出程序。

运行效果

以上仅供记录。可帮助理解vector。

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