Does placement-new introduce a sequence point?

Question

Consider the following line of code:

new (p++) T();

If the constructor T() throws an exception, is p guaranteed to have already been incremented?

Answer 1

From 5.3.4 [expr.new] (quoting from n3242):

11 The new-placement syntax is used to supply additional arguments to an allocation function. If used, overload resolution is performed on a function call created by assembling an argument list consisting of the amount of space requested (the first argument) and the expressions in the new-placement part of the new-expression (the second and succeeding arguments).

So in a new expression the allocation function is used from a function call (which makes sense). All allocation functions are functions, including the ones provided by the implementation, from 3.7.4.1 [basic.stc.dynamic.allocation]:

1 An allocation function shall be a class member function or a global function; [...]

So by the time an exception is thrown from the constructor, the allocation has taken place and the associated function call expression has been fully evaluated.

Answer 2

Yes it is guaranteed to be incremented.

The operators are just syntactic sugar for function/method calls.
I don't believe new has any special meaning above operator so it should be the same.

Thus all parameter are fully evaluated (with sequence point) before the function new is called.

Answer 3

I don't think the standard answers this question directly/explicitly. Implicitly, however, the answer is yes.

In particular, the placement syntax for new is simply a way of specifying extra parameters that will be passed to a function. Like any other function call, there is a sequence point between evaluating all the parameters to the function (in unspecified order), and executing any code in the function. I believe that should mean your p++ will be evaluated and all side effects applied before anything else happens.

Answer 4

Placement new is just a regular function, named operator new(size_t, void*) . It simply returns its second argument.

Answer 5

The increment operator does the following:

1. stores the old value in a internal copy
2. increments by one
3. returns the old value
4. deletes the copy of the old value

So, p is guaranteed to be incremented.