Monday, August 25, 2008

Naming convention used in Symbian

Why we require special "Naming convention" for symbian.

* provide common syntax for Symbian OS C++
* help reinforce Symbian OS programming idioms
* help communicate Symbian OS C++ class design for APIs
* serve as checklist for coding
* act as reference during code inspection/review
* helps produce efficient and reliable code for ROM-based devices

Fundamental data types in Symbian
* typedefs of built-in types for integer, floating-point, character, and pointer types (e32def.h), compiler-independent.
* TInt, TUint signed and unsigned 32-bit integers
* TBool, values ETrue (=1) and EFalse (=0)
* TReal, Double precision (64-bit) floating point number
* TText, Build independent general text character, In non-Unicode builds, this is mapped to TText8. In Unicode builds, this is mapped to TText16.
* TAny*, Pointer to anything (use instead of void*)

Symbian OS Classes
* Classes should have a clear role
* One class to one header file is recommended.
* Layout of header files:
#include files;
friend classes;
private methods;
public data.
* T-, C-, M-, R- convention to denote different class types

Types of Symbian.C++ classes

T Classes
* Behave like C++ built-in types
* No destructor => can be created on the stack and will be cleaned up correctly when the scope of function exits
* Contain member data which is:
-Built-in types
-Pointers and references with uses a relationship
* Contain all data internally
* Example:
          class TInitParams {
TInt iN1;
TInt iN2;
C Classes
* CBase (defined in e32base.h) is the base class for all C classes.
* All C objects are allocated on the heap.
* When it is first allocated on the heap all member data will be zero-filled
* When no longer needed heap-based objects must be destroyed
* It has a virtual destructor (destroyed properly by deletion through a CBase pointer)
* Example:
          class CExample : public CBase
R Classes
* R classes are proxies for objects usually owned elsewhere.
* There are two main motivations for this,
- the real object is owned by a server in a different thread or address space
-implementation of real object must be hidden from the client.
* There is no common base class for all R classes.
* The initialization function has a variety of names, like Open(), Create(), Allocate(), etc.
* The termination function has a variety of names, like Close(), Destroy(), Free(), etc.

M Classes
* The only form of multiple inheritance allowed by Symbian OS is where the extra classes are Mixins.
* Mixins (M classes), define an interface but do not provide an implementation of it
* they do not have any data members.
* only pure virtual functions
* A concrete class derived from a Mixin must implement its interface.
* Example:
class MRadio
virtual void TuneL() =0;

class MClock
virtual void CurrentTimeL(TTime& aTime) =0;

class CClockRadio : public CBase, public MRadio, public MClock
void TuneL();
void CurrentTimeL(TTime& aTime);
Class members

* Data members: use prefix i -, should be private
* Arguments: prefix a-
* variables start with lower case, Functions Start With Capitals
* Setter functions: SetThing(aThing);
* Getter functions: myThing = Thing(); (return it)
GetThing(myThing); (pass it by ref.)
* Variables including arguments: & for uses-a and * for has-a
* Trailing L,C for functions that cause exceptions (L means leave function, LC means it may leave and the function keep object on cleanupstuck)
* Trailing D for functions that delete object

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