[immodule-qt] keyword static of C++ (Re: Question about svn trunk)

[Zhe Su]

Hi,

static variable within a method are global for all class objects. It's
same as what's in C.

So you must store per-object (instance) data into class member.

Regards
James Su

On Wed, 11 Aug 2004 02:00:12 +0900, YamaKen <yamaken at bp.iij4u.or.jp> wrote:
> Hi all, this is my last TODO item currently doable. Please reply
> to any discussions to activate me :)
> 
> At Tue, 13 Jul 2004 02:46:53 +0900,
> yamaken at bp.iij4u.or.jp wrote:
> >
> > At Mon, 12 Jul 2004 23:19:18 +0900,
> > kaminmat at cc.rim.or.jp wrote:
> > >
> > > On Monday 12 July 2004 06:41, YamaKen wrote:
> > > > Probably you have forgotten the
> > > > code. QETWidget::translateKeyEventInternal() uses a static
> > > > variable instead of instance variable to store the state as
> > > > following, so lastWinId is required to prevent interwidget key
> > > > state transition.
> > >
> > > I understood that the static variable in a method was separately
> > > treated for each instance. lastWinId will be required if this understanding
> > > is wrong. Please commit the code.
> >
> > At least, gcc 3.3.3 showed that my understanding is correct. See
> > attached code and following result.
> >
> > $ gcc --version
> > gcc (GCC) 3.3.3 [FreeBSD] 20031106
> > $ ./a.out
> > 0xbfbfe7cf: initial
> > 0xbfbfe7ce: initial
> > 0xbfbfe7cf: a
> > 0xbfbfe7ce: a
> >
> > But I had recently seen some C++ codes based on your
> > understanding. Is it a new C++ feature? Or, is some famous
> > (wrong) explanation about it existing?
> 
> Daisuke and Cougar (and possibly Kazuki) are understanding
> static variable within a method as per-instance storage. But I
> can't imagine that such feature is a correct C++ specification
> because it breaks linker semantics or costs unnatural constructs
> through vptr.
> 
> I've investigated the C++ specification to verify this
> issue. But I've not found any description about such feature.
> 
> First I've updated my C++ specification doc from 'ISO/IEC 14882
> First edition 1998-09-01' to 'ISO/IEC 14882 Second edition
> 2003-10-15' by purchasing from ANSI eStandards Store.
> 
> http://webstore.ansi.org/ansidocstore/product.asp?sku=INCITS%2FISO%2FIEC+14882%2D2003
> 
> And I had read about the static. But I had found only
> traditional definitions about it. No other definitions around
> 'declared static' or 'keyword static' had been found by fulltext
> search.
> 
> ----------------------------------------------------------------
> 7 Declarations
> 7.1.1 Storage class specifiers
> 4 The static specifier can be applied only to names of objects
>   and functions and to anonymous unions (9.5). There can be no
>   static function declarations within a block, nor any static
>   function parameters. A static specifier used in the
>   declaration of an object declares the object to have static
>   storage duration (3.7.1). A static specifier can be used in
>   declarations of class members; 9.4 describes its effect. For
>   the linkage of a name declared with a static specifier, see
>   3.5.
> 
> 3.7 Storage duration
> 3.7.1 Static storage duration
> 1 All objects which neither have dynamic storage duration nor
>   are local have static storage duration. The storage for these
>   objects shall last for the duration of the program (3.6.2,
>   3.6.3).
> 
> 2 If an object of static storage duration has initialization or
>   a destructor with side effects, it shall not be eliminated
>   even if it appears to be unused, except that a class object or
>   its copy may be eliminated as specified in 12.8.
> 
> 3 The keyword static can be used to declare a local variable
>   with static storage duration. [Note: 6.7 describes the
>   initialization of local static variables; 3.6.3 describes the
>   destruction of local static variables. ]
> 
> 4 The keyword static applied to a class data member in a class
>   definition gives the data member static storage duration.
> ----------------------------------------------------------------
> 
> In addition, I had googled about this issue and found a wiki
> page.
> 
> Cpp Static Riddle
> http://c2.com/cgi/wiki?CppStaticRiddle
> 
> ----------------------------------------------------------------
> I've got a question on this topic. Is a static variable defined
> in a class method, similar to a member variable that has scope
> only for that method? In other words is a new static variable
> created for each instance of the class?
> 
> No, see above for the meaning of static method variable and
> static instance variable.
> ----------------------------------------------------------------
> 
> These two descriptions in this mail and the behavior of gcc
> 3.3.3 written in my previous mail are indicating that my
> understanding is right.
> 
> I want to rewrite some codes in our repository involving static
> variables if nobody shows me another information.
> 
> Anyone?
> 
> -------------------------------
> YamaKen  yamaken at bp.iij4u.or.jp
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