c++ primer plus阅读笔记12---手动调用析构函数

再谈定位new运算符

我们来看代码：

#include <iostream>
#include <string>
#include <new>
using namespace std;
const int BUF=512;
class JustTestting
{
private:
string words;
int number;
public:
JustTestting(const string &s="Just Testing",int n=0)
{
words=s;
number=n;
cout<<words<<" constructed\n";
}
~JustTestting()
{
cout<<words<<" destoryed\n";
}

void Show()const
{
cout<<words<<","<<number<<endl;
}
};

int main()
{
char *buffer=new char[BUF];

JustTestting *pc1,*pc2;
pc1=new(buffer)JustTestting;  //pc1在堆上buffer处
pc2=new JustTestting("Heap1",20);//pc2在堆上

cout<<"Memory block address\n"<<"buffer:"<<(void *)buffer<<" Heap:"<<pc2<<endl;
cout<<"Memory contents:\n";
cout<<pc1<<":";
pc1->Show();

cout<<pc2<<":";
pc2->Show();

JustTestting *pc3,*pc4;
pc3=new(buffer)JustTestting("Bad Idea",6);//pc３在堆上buffer处
pc4=new JustTestting("Heap2",10);　　//pc４在堆上
cout<<"Memory contents:\n";
cout<<pc3<<":";
pc3->Show();
cout<<pc4<<":";
pc4->Show();
//pc1-> ~JustTestting();　　delete pc
4000
1　pc3将会出错，这里需要手动调用pc1的析构函数
//pc3-> ~JustTestting();　

delete pc2;　　　　　
delete pc4;
delete []buffer;
cout<<"done\n";
return  0;

}

上边的代码中，pc1和pc3都在堆上申请的buffer中，当调用delete []buffer时，会将buffer处的内存全部释放，但是delete []buffer并不知道里边还有个对象，所以不会调用该对象的析构函数，为了调用其析构函数，必须手动调用，pc1-> ~JustTestting();