placenew2.cpp

一本很好的C++学习的丛书！初学者必看的

// placenew2.cpp  -- new, placement new, no delete
#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];       // get a block of memory

    JustTesting *pc1, *pc2;

    pc1 = new (buffer) JustTesting;      // place object in buffer
    pc2 = new JustTesting("Heap1", 20);  // place object on heap
    
    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, *pc4;
// fix placement new location
    pc3 = new (buffer + sizeof (JustTesting))
                JustTesting("Better Idea", 6);
    pc4 = new JustTesting("Heap2", 10);
    
    cout << "Memory contents:\n";
    cout << pc3 << ": ";
    pc3->Show();
    cout << pc4 << ": ";
    pc4->Show();
    
    delete pc2;           // free Heap1         
    delete pc4;           // free Heap2
// explicitly destroy placement new objects
    pc3->~JustTesting();  // destroy object pointed to by pc3
    pc1->~JustTesting();  // destroy object pointed to by pc1
    delete [] buffer;     // free buffer
    cout << "Done\n";
    return 0;
}