new basic knowledge

There are four parts of knowledge about new operator:
1. throw bad_alloc exception.
2. no throw, but return nullptr(since c++11)
3. placement new(not allocate, just ctor)
4. operator new(just allocate, no ctor)
MyClass * p1 = new MyClass;  //1: if fail, through bad_alloc

MyClass * p2 = new (std::nothrow) MyClass; //2: no throw

new (p2) MyClass;  //3: placement new
//4: operator new
MyClass * p3 = (MyClass*) ::operator new (sizeof(MyClass));
      // allocates memory by calling: operator new
      // but does not call MyClass’s ctor
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 []; Any time you want to use new to allocate an array, ask yourself if you can replace it with vector or string.