Re: Initializers

"Alf P. Steinbach" <>
Tue, 20 Apr 2010 10:36:26 +0200
* Michael Tsang:

I'm very confused among different types of initializations:


All that you need to remember and that you can rely on is

   * Static duration objects are zero initialized before anything else.

   * Apart from that, you get the initialization that you specify.

E.g. if you have defined at least one constructor for your class, then a
constructor will be called for every instance of that class (except if one does
nasty low-level things).

And e.g., when you write

   T* const p = new T();

then the parenthesis says that you want initialization, and for each member of T
you get the initialization that is available (zeroing or a constructor call).

If you omit the parenthesis then you say that you don't care about
initialization and that you will be happy with whatever initialization that T
defines, if any.


Also, how does zero-initializing a reference make sense?

The standard defines it thusly, in ?8.5/5: "no initialization is performed".

It's that simple.

Of course since you can't use the reference without UB before it's been properly
initialized, a compiler may choose to represent a namespace level reference as a
pointer and zero the pointer value so that &r, if it didn't do any of all the
arbitrary things that the UB allows, would yield a null-pointer at this time.

Cheers & hth.,

- Alf

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