#C++PrimerPlus# Chapter12_Exersice9_placenew2
上题中,使用定位new分配内存中存在两个问题。
1,pc3创建的时候覆盖掉了pc1,这是因为new对象时提供的地址(buffer)相同,应当给后创建的对象提供的地址一个偏移量sizeof(JustTesting);
2,delete [] buffer 未能调用定位new的两个对象pc1,pc3的析构函数,需要显式的调用他们。
程序清单如下:
// placenew2.cpp
#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() { cout << words << ", " << number << endl; }
};
int main()
{
char* buffer = new char[BUF];
JustTesting* pc1;
JustTesting* pc2;
pc1 = new (buffer) JustTesting;
pc2 = new JustTesting("Heap1", 20);
cout << "Memory block addresses:\n" << "buffer: " << (void*) buffer << " heap: " << pc2 << endl;
cout << "Memory contents:\n";
cout << pc1 << ": ";
pc1->Show();
cout << pc2 << ": ";
pc2->Show();
JustTesting* pc3;
JustTesting* pc4;
pc3 = new (buffer + sizeof(JustTesting)) JustTesting("Better Idea", 6);
pc4 = new JustTesting("Heap2", 10);
cout << "Memory contents:\n";
cout << pc3 << ": ";
pc1->Show();
cout << pc4 << ": ";
pc2->Show();
delete pc2;
delete pc4;
pc1->~JustTesting();
pc3->~JustTesting();
delete [] buffer;
cout << "Done\n";
system("pause>nul");
return 0;
}
结束。