Re: C++ Classes interaction

Posted by Fabrice_CBA on
URL: http://quantlib.414.s1.nabble.com/C-Classes-interaction-tp5550p5552.html

Thanks Toyin,

 

It all makes thanks now. I also googled "C++ Forward Declaration" as advised by Luigi (thanks for that), and found a few more explanations that I will share here with those interested.

 

    - When the size or actual content of a forward-casted classe is not important to the code, a forward declaration is sufficient, the header file need not be included in the .h or in the .cpp.

    - Forward declaration can be used for cyclic dependency between 2 classes.

    - Forward declaration is to be prefered to header inclusion when possible.

 

The last point makes me even more surprised not having heard of it before. I guess I'll have a talk with my C++ teachers...

 

Thanks,

Fabrice

 

---

From: Toyin Akin [mailto:[hidden email]]
Sent: Friday, 15 February 2008 7:21 PM
To: Lecuyer, Fabrice; [hidden email]
Subject: RE: [Quantlib-users] C++ Classes interaction

 
Hi Fabrice,
 
I haven't look at the code yet, but the declaration you see is called a forward declaration.
 
Basically if a class, within a header file, contains methods or class types that are represented as pointers or references then in order to tell the compiler the makeup of these types you can either include the header files of these types or you can forward declare the class types. In the latter case you will need to include the needed header files within the cpp file of the class you are implementing.
 
You will also need to add the needed header files to any other implementation file (cpp or maybe even hpp files if you implement methods inline) that includes this header file.
 
The forward declare approach is a bit like, here's a type, but I'll tell you the makeup of it later on when it's actually used (within methods usually).
 
You cannot used the forward declare methodology if you are actually passing the types explicitly (not a pointer or reference). The compiler needs to know the definition in this case.
 
The forward declare approach really shortens the length of compilation (especially if the header files are edited frequency).
 
Regards,
Toyin Akin.


 

---

Date: Fri, 15 Feb 2008 18:05:37 +1100
From: [hidden email]
To: [hidden email]
Subject: [Quantlib-users] C++ Classes interaction

Hi all,

 

I apologize in advance for the "newbie" taste of my question.

I was digging in the market model code and found something of the form:

//////////////////////////////////////////////////////////////////////////////////

namespace QuantLib {
class CMSwapCurveState;
//! Drift computation for CMS market models
/*! Returns the drift \f$ \mu \Delta t \f$.
See Mark Joshi, <i>Rapid Computation of Drifts in a
Reduced Factor Libor Market Model</i>, Wilmott Magazine,
May 2003.
*/
class CMSMMDriftCalculator {
public:
...
///////////////////////////////////////////////////////////////////////////
I found that in many other classes.

Could someone explain me very quickly what does this "class CMSwapCurveState" syntax do? If it's a way for the two classes to interact with each other, why isn't the key word "friend" used?

Furthermore, this is done before the class definition, how does the compiler understand that they are linked?

If you could point me to a C++ tutorial that explains this, since I failed to find any explanation about this syntax.

 

Thanks,

Fabrice

 __________________________________________________
 Commonwealth Bank
 Fabrice Lecuyer 
 Quantitative Analyst
 Global Market & Treasury
 

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