Concept

• Static allocation
  The compiler allocates memory in stack space for objects.Using this method, the constructor of the class is called directly.For example:

A a

• Dynamic build
  Allocate memory in heap space.This process is divided into two steps:
  [first step] execute the operator new( ) function to allocate memory in the heap space;
  [second step] call the class constructor to construct the object.

Static allocation

Ideas

• To restrict the new operator to implement class objects can only be created on the stack.This restricts the class object from calling the new operator.

class A {private:void* operator new(size_t t){} //Set as privatevoid operator delete(void* ptr){} //If new is overloaded, delete needs to be overloaded.Corresponds to overloading.public:A(){}~A(){}};

Dynamic allocation

There are a few points to note.

• Only allowing dynamic allocation requires disallowing direct calls to constructors.But the constructor needs to be called indirectly, so the constructor cannot be made private.
• When the compiler allocates stack space for a class object, it will first check the accessibility of the class's destructor (in fact, not only the destructor, but as long as it is a non-static function, the compiler willan examination).If the class's destructor is not accessible outside the class, the compiler refuses to allocate memory for the class object on stack space.This also disables static allocation.Therefore, destructors can be defined as private.
• Because the destructor is defined as private, an additional destructor needs to be defined to release memory.

class A {public:A(){}void destory(){delete this;}private:~A(){}};