Singleton and static function

[John Doe]

Hi,

I have a singleton class defined like this :

class UIManager : public CSingleton<UIManager>,
public CObject
{
protected:
DECLARE_DYNAMIC(UIManager)
friend class CSingleton<UIManager>;

UIManager();
virtual ~UIManager();

public:
...
};

and I was using this code like this :

A)
UIManager* l_pUiMgr = UIManager::GetInstance();
ASSERT (l_pUiMgr != NULL);
l_pUiMgr->GetResText( a_ResId, bStripHtml);

But I was fed up with always typing this so I have declared below my
UIManager class a static function :

static inline UIManager& UIManager() { return *(UIManager::GetInstance()); }

and I wanted to be able to call it like that :

UIManager().GetResText( a_ResId, bStripHtml);

The problem is I get some compilations errors with the code in A)

5>c:\wce_v42\inc\BaseView.h(227) : error C2065: 'l_pUiMgr' : undeclared
identifier

Why I cannot write UIManager* now ?

[Maxim Yegorushkin]

On Oct 31, 3:27 pm, John Doe <mos...@anonymous.org> wrote:
> Hi,
>
> I have a singleton class defined like this :
>
> class UIManager : public CSingleton<UIManager>,
>                                   public CObject
> {
> protected:
>         DECLARE_DYNAMIC(UIManager)
>         friend class CSingleton<UIManager>;
>
>         UIManager();
>         virtual ~UIManager();
>
> public:
> ...
>
> };

What do you need that CSingleton<> for? Can you not just have a global
object?

> and I was using this code like this :
>
> A)
> UIManager* l_pUiMgr = UIManager::GetInstance();
> ASSERT (l_pUiMgr != NULL);
> l_pUiMgr->GetResText( a_ResId, bStripHtml);

That ASSERT is probably useless because if UIManager is allocated on
the heap (using new) it throws an exception. It it it allocated as a
function static variable, than it can never be NULL.

> But I was fed up with always typing this so I have declared below my
> UIManager class a static function :
>
> static inline UIManager& UIManager() { return *(UIManager::GetInstance()); }
>
> and I wanted to be able to call it like that :
>
> UIManager().GetResText( a_ResId, bStripHtml);

Which looks better.

> The problem is I get some compilations errors with the code in A)
>
> 5>c:\wce_v42\inc\BaseView.h(227) : error C2065: 'l_pUiMgr' : undeclared
> identifier
>
> Why I cannot write UIManager* now ?

This error says that you are accessing l_pUiMgr object, which is not
available from the current scope. Either you misspelled it or did not
include the necessary header files.

--
Max

[Salt_Peter]

Why don't you tell us? l_pUiMgr is an undeclared identifier. You are
doing something wrong, what that might be we don't know. Put together
a simple, compileable case forth without MS-specific macros.

[Mosfet]

Salt_Peter a écrit :

I mean that the following line doesn't compile anymore :

UIManager* l_pUiMgr = UIManager::GetInstance();

but maybe I forgot one include ...

[Salt_Peter]

> but maybe I forgot one include ...- Hide quoted text -
>
> - Show quoted text -

I had no problem, then again, i don't need MS code to do any of it.
i'ld suggest declaring a pointer only (which does not construct
anything) just to find out if UIManager is recognized as a complete
type.

UIManager* p_mgr;

If that fails then includes are indeed the issue and you should get an
error specifically stating what is not recognized as a known type. I
have no clue what header CSingleton is found in (only a Singleton can
access UIManager's protected constructor).

I will say that your setup should look like the following, which does
work, although my Singleton type needs a little more tightening to
prevent side-effects.

[OT]
MS and MFC as well as other languages like Java live in an 'everything
is an Object or CObject' world. As if an instance was somehow
otherwise NOT an object. That mentality is bad, nasty, buggy, insane,
dumb, stupid, etc.
[/OT]

#include <iostream>

class Object { };

template< typename T >
class Singleton
{
protected:
Singleton() { std::cout << "Singleton()\n"; }
~Singleton() { std::cout << "~Singleton()\n"; }
private:
Singleton(const Singleton& copy);
Singleton& operator= (const Singleton&);
public:
static T* const GetInstance()
{
static T t;
std::cout << "&t = " << &t << std::endl;
return &t;
}
};

class Manager : public Singleton< Manager >, public Object
{
friend class Singleton<Manager>;
protected:
Manager() { std::cout << "Manager()\n"; }
virtual ~Manager() { std::cout << "~Manager()\n"; }
};

int main()
{
Manager* p_mgr = Manager::GetInstance();
std::cout << "Manager* p_mgr = ";
std::cout << p_mgr << std::endl;
}