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[Anders Logg <logg@xxxxxxxxx>]

So the conclusion is that for a class that has a default constructor, there is absolutely no difference. But I would be more comfortable if the () were included. 

--
Anders

20 aug 2012 kl. 23:38 skrev Benjamin Kehlet <benjamik@xxxxxxxxx>:

> 2012/8/20 Anders Logg <logg@xxxxxxxxx>:
>> On Mon, Aug 20, 2012 at 05:00:32PM +0100, Garth N. Wells wrote:
>>> On 20 August 2012 16:50, Anders Logg <logg@xxxxxxxxx> wrote:
>>>> I'm editing the linear algebra interface to add support for generic
>>>> Krylov matrices and I'm seeing things like this:
>>>> 
>>>> 
>>>>    /// Create empty vector (global)
>>>>    boost::shared_ptr<GenericVector> create_vector() const
>>>>    {
>>>>      boost::shared_ptr<GenericVector> x(new MTL4Vector);
>>>>      return x;
>>>>    }
>>>> 
>>>>    /// Create empty vector (local)o
>>>>    boost::shared_ptr<GenericVector> create_local_vector() const
>>>>    {
>>>>      boost::shared_ptr<GenericVector> x(new MTL4Vector);
>>>>      return x;
>>>>    }
>>>> 
>>>> I thought () was required:
>>>> 
>>>>    boost::shared_ptr<GenericVector> x(new MTL4Vector());
>>>> 
>>>> Has this always been the case?
>>>> 
>>> 
>>> There are some instances where we need to distinguish between local
>>> and distributed vectors, notably in the PETSc interface code. To work
>>> through GenericVector, it appears in the MTL, uBLAS, etc code too.
>> 
>> I know, I wasn't referring to the global vs local. I meant omitting
>> the () in constructors that take no arguments:
>> 
>>  new MTL4Vector()
>> 
>> vs
>> 
>>  new MTL4Vector
> 
> Cases exist where the behaviour will be different, but they are rare.
> 
> Compare
> http://en.cppreference.com/w/cpp/language/default_initialization
> with
> http://en.cppreference.com/w/cpp/language/value_initialization
> 
> (Some examples are given in this answer: http://stackoverflow.com/a/620402 )
> 
> Benjamin
> 
>> 
>> --
>> Anders
>> 
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