当类中定义了自定义的new操作符时，编译器会调用这个操作符来分配类的实例所需的内存。当派生类也定义了自己的new操作符时，派生类对象在实例化时会调用派生类的new操作符。这里是一个示例：

#include 
#include 

using namespace std;

class Base {
public:
   void *operator new(size_t size) {
      cout << "Calling Base::new " << endl;
      void *p = malloc(size);
      return p;
   }
   void operator delete(void *p) {
      cout << "Calling Base::delete " << endl;
      free(p);
   }
};

class Derived: public Base {
public:
   void *operator new(size_t size) {
      cout << "Calling Derived::new " << endl;
      void *p = malloc(size);
      return p;
   }
   void operator delete(void *p) {
      cout << "Calling Derived::delete " << endl;
      free(p);
   }
};

int main() {
   Base *b = new Base();
   Derived *d = new Derived();
   delete b;
   delete d;

   return 0;
}

输出结果如下：

Calling Base::new 
Calling Derived::new 
Calling Base::delete 
Calling Derived::delete 

可以看到，派生类中的new操作符覆盖了基类中的new操作符，因此在创建Derived对象时，会调用Derived的new操作符。但在删除对象时，仍然会调用基类的delete操作符，因为Derived没有覆盖基类的delete操作符。