[Bug c++/33916] Default constructor fails to initialize array members

["crowl at google dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #1 from crowl at google dot com  2007-10-31 20:08 -------
The wording in the C++ standard working paper is as follows:

8.5 Initializers [dcl.init]

-8- An object whose initializer is an empty set of parentheses, i.e.,
   (), shall be value-initialized.

Therefore, in <<< Stats my_stats = Stats(); >>>, the temporary object
is value-initialized and then my_stats is copy-constructed.

-5- To value-initialize an object of type T means:
   -- if T is a non-union class type without a user-provided
      constructor, then every non-static data member and base-class
      component of T is value-initialized;93)

   93) Value-initialization for such a class object may be
       implemented by zero-initializing the object and then calling
       the default constructor.

   -- if T is an array type, then each element is value-initialized;

   -- otherwise, the object is zero-initialized

Therefore, the temporary should be zero-initialized and the resulting
copy should copy zeros.  So, I conclude that gcc 4.2.1 is in error.
(I suspect the compiler already eliminates the copy.)

I suspect the problem arose in someone thinking that the zero
initialization in front of a call to a default constructor was
redundant.  Alas, it is not.  It is redundant only if the constructor
initializes all fields, which is generally unknowable, though the
compiler could determine so for many types and constructors.


-- 

crowl at google dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |crowl at google dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916