Question

I saw code like this:

void *NewElts = operator new(NewCapacityInBytes);

And matching call explicitly operator delete is used consequent later.

Why do this instead of:

void *NewElts = new char[NewCapacityInBytes];

Why explicit call to operator new and operator delete??

Answer 1

Explicitly calling operator new like that calls the global “raw” operator new. Global operator new returns a raw memory block without calling the object’s constructor or any user-defined overloads of new. So basically, global operator new is similar to malloc from C.

So:

// Allocates space for a T, and calls T's constructor,
// or calls a user-defined overload of new.
//
T* v = new T;

// Allocates space for N instances of T, and calls T's 
// constructor on each, or calls a user-defined overload
// of new[]
//
T* v = new T[N];

// Simply returns a raw byte array of `sizeof(T)` bytes.
// No constructor is invoked.
//
void* v = ::operator new(sizeof(T));