Item 49: Understand the Behavior of the new-Handler

operator new will repeatedly(!) call new-handler until it can find enough space.

An new-handler could do one of the following:

• Make more space available
• Install a different new-handler
• Deinstall the new-handler (operator new will throw an exception when there is no new-handler)
• Not return

Nice trick: Use templatized base class with static data member so that each derived class has different instantiated base class and its own static data member (this is called curiously recurring template pattern (CRTP)).

(By the way, what if memory must be dynamically allocated when you are writing error message to cerr…)

History: Until 1993 C++ requires operator new returns null when it can’t allocate space, but now it should throw bad_alloc exception. To preserve this legacy, C++ provides a nothrow form new:

new (std::nothrow) Foo;

But note that it doesn’t mean it provides the nothrow exception guarantee, it only means the allocation part (operator new) doesn’t throw, but doesn’t mean the constructor won’t throw.