该程序使用定位 new运算符在相邻的内存单元中创建两个对象,并调用了合适的析构函数。
#pragma region 12.9 placenew2.cpp
//placenew2.cpp -- new placement new,no delete
#if 1
#include <iostream>
#include <string>
#include<new>
using namespace std;
const int BUF = 512;
class JustTesting
{
private:
string words;
int number;
public:
JustTesting(const string& s = "Just Testing", int n = 0)
{
words = s; number = n; cout << words << " constructed\n";
}
~JustTesting() { cout << words << " destroyed\n"; }
void Show()const { cout << words << ", " << number << endl; }
};
int main()
{
char* buffer = new char[BUF];
JustTesting* pc1, * pc2;
pc1 = new (buffer)JustTesting;
pc2 = new JustTesting("heap1", 20);
cout << endl << "memory block address:\n" << "buffer: "
<< (void*)buffer << " heap: " << pc2 << endl << endl;
cout << "Memory contents:\n";
cout << pc1 << ": ";
pc1->Show();
cout << pc2 << ": ";
pc2->Show();
cout << endl;
JustTesting* pc3, * pc4;
//控制偏移
pc3 = new(buffer + sizeof(JustTesting))JustTesting("Bad Idea", 6);
pc4 = new JustTesting("Heap2", 10);
cout << endl << "Memory contents:\n";
cout << pc3 << ": ";
pc3->Show();
cout << pc4 << ": ";
pc4->Show();
delete pc2; //free heap1,heap2;
delete pc4;
//释放顺序和申请顺序相反
pc3->~JustTesting();
pc1->~JustTesting();
delete[]buffer; //free buffer;
cout << "Done\n";
return 0;
}
#endif
#pragma endregion
总结:
1,从从而是看,在buffer中申请的地址是不一样的。
2,四个对象的析构函数都得到了释放
3,delete的顺序和new的顺序相反,最后new的最先delete