c++ - Difference between 'new operator' and 'operator new'?

Question

What is difference between "new operator" and "operator new"?

Answer 1

I usually try to phrase things differently to differentiate between the two a bit better, but it's a good question in any case.

Operator new is a function that allocates raw memory -- at least conceptually, it's not much different from malloc(). Though it's fairly unusual unless you're writing something like your own container, you can call operator new directly, like:

char *x = static_cast<char *>(operator new(100));

It's also possible to overload operator new either globally, or for a specific class. IIRC, the signature is:

void *operator new(size_t);

Of course, if you overload an operator new (either global or for a class), you'll also want/need to overload the matching operator delete as well. For what it's worth, there's also a separate operator new[] that's used to allocate memory for arrays -- but you're almost certainly better off ignoring that whole mess completely.

The new operator is what you normally use to create an object from the free store:

my_class *x = new my_class(0);

The difference between the two is that operator new just allocates raw memory, nothing else. The new operator starts by using operator new to allocate memory, but then it invokes the constructor for the right type of object, so the result is a real live object created in that memory. If that object contains any other objects (either embedded or as base classes) those constructors as invoked as well.