How to initialise memory with new operator in C++?

Question

I'm just beginning to get into C++ and I want to pick up some good habits. If I have just allocated an array of type int with the new operator, how can I initialise them all to 0 without looping through them all myself? Should I just use memset? Is there a “C++” way to do it?

Answer 1

It's a surprisingly little-known feature of C++ (as evidenced by the fact that no-one has given this as an answer yet), but it actually has special syntax for value-initializing an array:

new int[10]();

Note that you must use the empty parentheses — you cannot, for example, use (0) or anything else (which is why this is only useful for value initialization).

This is explicitly permitted by ISO C++03 5.3.4[expr.new]/15, which says:

A new-expression that creates an object of type T initializes that object as follows:

...

• If the new-initializer is of the form (), the item is value-initialized (8.5);

and does not restrict the types for which this is allowed, whereas the (expression-list) form is explicitly restricted by further rules in the same section such that it does not allow array types.