newplace.cpp

来自「一本很好的C++学习的丛书！初学者必看的」· C++ 代码 · 共 57 行

// newplace.cpp -- using placement new
#include <iostream>
#include <new>         // for placement new
const int BUF = 512;
const int N = 5;
char buffer[BUF];      // chunk of memory
int main()
{
    using namespace std;

    double *pd1, *pd2;
    int i;
    cout << "Calling new and placement new:\n";
    pd1 = new double[N];           // use heap
    pd2 = new (buffer) double[N];  // use buffer array
    for (i = 0; i < N; i++)
        pd2[i] = pd1[i] = 1000 + 20.0 * i;
    cout << "Buffer addresses:\n" << "  heap: " << pd1
        << "  static: " << (void *) buffer  <<endl;
    cout << "Buffer contents:\n";
    for (i = 0; i < N; i++)
    {
        cout << pd1[i] << " at " << &pd1[i] << "; ";
        cout << pd2[i] << " at " << &pd2[i] << endl;
    }

    cout << "\nCalling new and placement new a second time:\n";
    double *pd3, *pd4;
    pd3= new double[N];
    pd4 = new (buffer) double[N];
    for (i = 0; i < N; i++)
        pd4[i] = pd3[i] = 1000 + 20.0 * i;
    cout << "Buffer contents:\n";
    for (i = 0; i < N; i++)
    {
        cout << pd3[i] << " at " << &pd3[i] << "; ";
        cout << pd4[i] << " at " << &pd4[i] << endl;
    }

    cout << "\nCalling new and placement new a third time:\n";
    delete [] pd1;
    pd1= new double[N];
    pd2 = new (buffer + N * sizeof(double)) double[N];
    for (i = 0; i < N; i++)
        pd2[i] = pd1[i] = 1000 + 20.0 * i;
    cout << "Buffer contents:\n";
    for (i = 0; i < N; i++)
    {
        cout << pd1[i] << " at " << &pd1[i] << "; ";
        cout << pd2[i] << " at " << &pd2[i] << endl;
    }
    delete [] pd1;
    delete [] pd3;

    return 0;
}