在固定位置new一个对象源代码

// usenew.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <new>
using namespace std;
class CNew
{
public:
	CNew(int nVal)
	{
		m_nData = nVal;
		cout << "constructor of CNew has been called!" << endl;
	}
	~CNew()
	{
		cout << "destructor of CNew has been called!" << endl;
	}
public:
	void PrintInfo()
	{
		cout << "data = " << m_nData << endl;
	}
private:
	int	m_nData;
};

void TestForNew();
char g_szBuf[300] = {0}; //stack memory
int _tmain(int argc, _TCHAR* argv[])
{
	memset(g_szBuf, 0, sizeof(g_szBuf));
	
	TestForNew();
	return 0;
}
void TestForNew()
{
	//1. 预分配缓冲
	char* pszBuf = new char[sizeof(CNew)];//new memory	
	if (NULL == pszBuf)
	{
		cout << "get memory failed..." << endl;
		return;
	}
	memset(pszBuf, 0, sizeof(CNew));	
	//2. 使用 placement new
	CNew* pNew = new(pszBuf) CNew(123);
	CNew* pNewTemp = new(g_szBuf) CNew(456);
	//使用对象
	pNew->PrintInfo();
	pNewTemp->PrintInfo();
	//3. 显式调用析构函数
	pNew->~CNew();
	pNewTemp->~CNew();
	//4. 释放预定义的缓冲
	if (NULL != pszBuf)
	{
		delete[] pszBuf;
		pszBuf = NULL;
	}
}