1.1.3.1 new basic knowledge

• There are four usage of new: 1) throw bad_alloc exception. 2) no throw, but return nullptr(sinnce c++11) 3)placement New(not allocate, just cotr) 4)operator new(just allocate, no ctor)
  MyClass * p1 = new MyClass;  //1: normal 
   
  MyClass * p2 = new (std::nothrow) MyClass; //2: no throw 
   
  new (p2) MyClass;  //3: placement new 
   
  MyClass * p3 = (MyClass*) ::operator new (sizeof(MyClass)); 
        // allocates memory by calling: operator new (sizeof(MyClass)) 
        // but does not call MyClass’s constructor
• new will call constructor function of a class, but malloc will not call constructor function. So in C++, you should use new instead of malloc.
• If you use new int[100], use delete [];
• Use set_new_handler function. When memory allocate failed, it will call this "callback" function.
  void noMemory(){ 
  cerr<<"␣New␣fail"<<endl 
  abort(); 
  } 
  //in the beginning of main() function. 
  set_new_handler(noMemory)
• In you customized error_handler Just for your certain class. You can’t call set_new_handle in main, it will affect all the new in global scope. You should overwrite you own operator new in your class. like below:
  void * X::operator new(size_t size){ 
  PEFH currentHandler = ::set_new_handler(currentPEHF) 
  void *memory = ::new char[size]; 
  ::set_new_handler(currentHandler); 
  return memory; 
  }
• construct an object in memory you’ve already got a pointer to ,use placement new. If you use placement new to create an object in some memory, you should avoid using the delete operator on that memory. Detail can be seen in C++ primer
  p1 = new(buffer) FOO(); 
  p2 = new(buffer+sizeof(FOO) ) FOO(); 
   
  p1->~FOO(); 
  p2->~FOO(); 
   
  delete[] buffer;