布局new分配 ，

布局new和普通New不同，相当于建立一个小堆空间 。

#include <iostream>
#include <string>
#include <new>
using namespace std;
const int BUF = 512;
class testing
{
private :
    string word;
    int len;
public:
    testing(const string & s = "tesing",int n = 0 )
    {
        word = s;
        len = n;
        cout <<word <<"construted"<<endl;
    }
    ~testing()
    {
        cout << word <<"destroy" <<endl;
    }
    void show() const
    {
        cout << word <<"," <<len <<endl;
    }
};

int main()
{
    char *buffer = new char[BUF];
    testing *pc1,*pc2;
    pc1 = new( buffer) testing;
    pc2 = new testing("heap1" , 20);

    cout <<"memory block address :" <<(void *)buffer << "heap1" << pc2<<endl;

    cout <<"memory content" << pc1 <<":";
        pc1->show();
    cout << pc2 <<":";
    pc2->show();

    testing *p3 , *p4;
    p3  = new (buffer + sizeof(testing)) testing("third",3);
    delete pc2;
     pc1->~testing();
     p3->~testing();
    delete [] buffer;
    return 0;
}