C++中placementnew操作符使用方法-创新互联

C++ 中placement new 操作符使用方法

placement new操作符能够在分配内存时指定内存位置。下面的程序使用了placement new操作符和常规new操作符给对象分配内存。

// placenew.cpp -- new, placement new, no delete
#include 
#include 
#include 

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

  JustTesting *pc3, *pc4;
  pc3 = new (buffer) JustTesting("bad 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
  delete [] buffer;  // free buffer
  cout << "Done\n";

  return 0;
}

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