must class member initialization lists in c++ be complete? or can they simply initialize one or two of the member data in a class?
thanks in advance!
+5
A:
They don't have to be complete. You can leave out base classes and non-POD class types that are default constructible, POD-types however will be left uninitialized.
Obviously constant members and references have to be initialized in the member initialization list.
Georg Fritzsche
2010-07-22 22:53:24
is there a difference between what the member initialization list does and what initializing variables through default constructors does, other than efficiency?
alphacentauri
2010-07-22 22:57:05
@alpha: What do you mean "through the default constructor"? At this stage, you shouldn't really be worried about efficiency anyway but correctness of code.
GMan
2010-07-22 22:58:45
@alpha: If you mean explicit vs. implicit default construction/initialization - there is only a difference for those types that would be left uninitialized.
Georg Fritzsche
2010-07-22 23:03:48
@alphacentauri: The question make so sense. You can use initialization list in default constructor. Your question suggest that they are mutually exclusive, which is not true.
AndreyT
2010-07-22 23:06:59
i was wondering or not initializing data in a default ctor has the same effect as using a member initialization list. I remember hearing somewhere that initialization and assignemt are not the same thing
alphacentauri
2010-07-22 23:16:56
Do you mean *assign values* in the constructor body? You can use a member initialization list (MIL) in the constructor: `foo::foo() : MLI {}`.
GMan
2010-07-22 23:23:20
@alpha: I think an example of what you mean would help.
Georg Fritzsche
2010-07-22 23:44:17
A:
No, they don't have to be complete - any members which aren't specified in it will be default-constructed (this includes any base classes).
Obviously, any members which aren't default-constructible must be explicitly initialised. And a small gotcha - types like integers or floats etc will not be initialised, so their initial value will be undefined.
Peter
2010-07-22 22:55:07
Not true in general. Members that aren't specified will be processed (or not) in accordance with their specific rules. For example, members of type `int` will be left uninitialized. To say that they will be "default-constructed" is incorrect. You can't "construct" and `int`. It has no constructor.
AndreyT
2010-07-22 23:04:55