Re: [deal.II] Re: Little question about constructor

[yuesu jin]

Dear Konrad,
  Appreciating for your detailed explanation, it really helps!! Thank you!
I am learning c++ by the means of studying deal.ii, so actually I am a
layman both in deal.ii and c++. I will read the reference page and books
you recommended. Thanks again!!
Best regards,
Yuesu

On Wed, Sep 4, 2019 at 5:03 AM Konrad  wrote:

> Hi Yuesu,
>
> I think this is rather a general C++ question. Once you create an object
> all members are initialized by invoking a constructor. If you do not
> declare any constructor the compiler will silently generate a set of
> constructors. The default constructor that takes no arguments is one of
> them. This will initialize all members in the order they are given. If you
> have a member of a primitive type like double or int memory for an int or
> double will be reserved (but not initialized with a value yet). If you have
> a class member it also needs to be initialized somehow so the compiler will
> look for a default constructor.
>
> What happens in your example is that the triangulation actually does get
> initialized by invoking its default constructor which initializes an empty
> triangulation. The dof_handler then can be called with the triangulation as
> an argument to store a (smart) pointer to the triangulation.
>
> See this documentation for example:
>
>
> https://docs.microsoft.com/en-us/cpp/cpp/constructors-cpp?view=vs-2019#constructors_in_composite_classes
>
> It is often good to know what the C++ compiler (secretly) does without
> explicitly telling you and what functions it generates if you do not
> provide them explicitly (and when you must do so). I really recommend the
> book by Scott Meyers "Effective C++: 55 ways ..."
>
> Hope that helps.
>
> Best,
> Konrad
>
>
> On Wednesday, September 4, 2019 at 4:44:24 AM UTC+2, yuesu jin wrote:
>>
>> Hi all,
>>
>>   I have a question about the constructor initialization list. In some
>> tutorials, we initialize the dof_handler in the constructor with parameter
>> triangulation, however, the triangulation is initialized in some member
>> function within this class, which means when we initialize the class, we
>> have not had the triangulation yet, I don't know why this method works?
>>
>> Best regards,
>> Yuesu
>>
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> 
> .
>


-- 
Yuesu Jin,
Ph.D student,
University of Houston,
College of Natural Sciences and Mathematics,
Department of Earth and Atmospheric Sciences,
Houston, Texas 77204-5008
346-404-2062

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[deal.II] Re: Little question about constructor

[Konrad]

Hi Yuesu,

I think this is rather a general C++ question. Once you create an object 
all members are initialized by invoking a constructor. If you do not 
declare any constructor the compiler will silently generate a set of 
constructors. The default constructor that takes no arguments is one of 
them. This will initialize all members in the order they are given. If you 
have a member of a primitive type like double or int memory for an int or 
double will be reserved (but not initialized with a value yet). If you have 
a class member it also needs to be initialized somehow so the compiler will 
look for a default constructor.

What happens in your example is that the triangulation actually does get 
initialized by invoking its default constructor which initializes an empty 
triangulation. The dof_handler then can be called with the triangulation as 
an argument to store a (smart) pointer to the triangulation.

See this documentation for example:

https://docs.microsoft.com/en-us/cpp/cpp/constructors-cpp?view=vs-2019#constructors_in_composite_classes

It is often good to know what the C++ compiler (secretly) does without 
explicitly telling you and what functions it generates if you do not 
provide them explicitly (and when you must do so). I really recommend the 
book by Scott Meyers "Effective C++: 55 ways ..."

Hope that helps.

Best,
Konrad


On Wednesday, September 4, 2019 at 4:44:24 AM UTC+2, yuesu jin wrote:
>
> Hi all,
>
>   I have a question about the constructor initialization list. In some 
> tutorials, we initialize the dof_handler in the constructor with parameter 
> triangulation, however, the triangulation is initialized in some member 
> function within this class, which means when we initialize the class, we 
> have not had the triangulation yet, I don't know why this method works?
>
> Best regards,
> Yuesu 
>

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