C++中的::operator new, ::operator delete

一般在使用new 和 delete的时候，做了两件事情，一是空间的配置（ new 是分配,delete是回收），而是调用对象的析构函数

但是也有办法将这两个过程分开

那就是显式的调用::operator new, ::operator delete，它们只进行空间配置，并不调用对象的析构函数

具体的可以参看下面这个例子：

// operator new[] example
#include <iostream>     // std::cout
#include <new>          // ::operator new[]

struct MyClass {
  int data;
  MyClass() {std::cout << '*';}  // print an asterisk for each construction
};

int main () {
  std::cout << "constructions (1): ";
  // allocates and constructs five objects:
  MyClass * p1 = new MyClass[5];
  std::cout << '
';

  std::cout << "constructions (2): ";
  // allocates and constructs five objects (nothrow):
  MyClass * p2 = new (std::nothrow) MyClass[5];
  std::cout << '
';

  std::cout << "constructions (3): ";
  // allocates storage for five objects, but does not construct them:
  MyClass * p3 = static_cast<MyClass*> (::operator new (sizeof(MyClass[5])));
  std::cout << '
';

  std::cout << "constructions (4): ";
  // constructs five objects at p3, but does not allocate:
  new (p3) MyClass[5];
  std::cout << '
';

  delete[] p3;
  delete[] p2;
  delete[] p1;

  return 0;
}

Edit & Run

关于operator delete和operator new ，可以参看这里的原型定义：

http://en.cppreference.com/w/cpp/memory/new/operator_delete

http://en.cppreference.com/w/cpp/memory/new/operator_new

可以看到，都是void*型的指针，跟C语言里面的malloc free机制差不多了。