What is the difference between the following 2 two initializations?
class Pod { public: int a, b; }; Pod *p1 = new Pod; Pod *p2 = new Pod(); 
- As JamesMcLaughlin said, no difference, furthermore that's not limited to PODs.MFH– MFH2013-03-17 02:16:42 +00:00Commented Mar 17, 2013 at 2:16
- @DavidRodríguez-dribeas How so?James M– James M2013-03-17 02:17:27 +00:00Commented Mar 17, 2013 at 2:17
- @JamesMcLaughlin: Read section 8.5 in the standard :)David Rodríguez - dribeas– David Rodríguez - dribeas2013-03-17 02:18:02 +00:00Commented Mar 17, 2013 at 2:18
- @DavidRodríguez-dribeas Yep, looks like I was wrong! Thanks.James M– James M2013-03-17 02:21:02 +00:00Commented Mar 17, 2013 at 2:21
- 1This previous thread explains zero, default and value-initialized and has examples stackoverflow.com/questions/1613341/…Shafik Yaghmour– Shafik Yaghmour2013-03-17 02:41:48 +00:00Commented Mar 17, 2013 at 2:41
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1 Answer
In the first case the object is left uninitialized, while in the second case the object is guaranteed to be value-initialized, which in this case as the type is POD it means zero-initialized
answered Mar 17, 2013 at 2:16
David Rodríguez - dribeas
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5 Comments
Jerry Coffin
Though the difference is essentially nonexistent in the case of
int, in the first case the members are default initialized rather than uninitialized.
David Rodríguez - dribeas
@JerryCoffin: Yes I should have been clearer, that part is also due to the fact that it is a POD, for which default-initialization means that the object is left uninitialized
Jerry Coffin
@DavidRodríguez-dribeas: ...but in C++11, it's not restricted to POD types either (IIRC, it should apply to the somewhat broader category of all trivially copyable types).
David Rodríguez - dribeas
@JerryCoffin: trivially copyable types? Not sure how that would matter here (there are no copies anywhere) and I cannot find a reference in n3777 that supports that. For value-initialization the distinction is between a class type with/without user provided default constructor. For default-initialization of a class type it implies calling the default constructor, which if defined implicitly will recursively cause default-initialization of the members... at the end members of fundamental types are left uninitialized
Jerry Coffin
@DavidRodríguez-dribeas: Copying isn't really relevant, but being trivially copyable is a looser requirement than being POD, and you don't have to meet the extra requirements to be POD for default initialization to mean leaving uninitialized.