Another problem with singleton...

[Manuel]

This is the singleton I'm trying to write:

global.h
----------------------------------------
class Global
{
int i;
static Global glob;
//Global(int x): i(x) { } ;
Global();
Global& operator=(Globa l&); // Disallowed
Global(const Global&); // Disallowed

//some global variables
int myVar;

public:
static Global& instance() { return glob; }

//some set variables
void setmyVar(int);

//some get functions
int getmyVar();

};
-----------------------------------------

global.cpp
-----------------------------------------
#include "global.h"

//Set functions
void Global::setmyVa r(int i){myVar = i;}

//Get functions
int Global::getmyVa r(){return myVar;}
-----------------------------------------


I'm trying to use the default constructor. But using it,
with this init in application code:
--------------------------------------------
Global Global::glob;
Global& GlobalVariables = Global::instanc e();
--------------------------------------------

The compiler return a linker error:

[Linker error] undefined reference to `Global::Global ()'


If I modify the global.h, using a constructor with arguments, like

Global(int x): i(x) { } ;

instead

Global();

and in application code write this init:

Global Global::glob(1) ;
Global& GlobalVariables = Global::instanc e();

it work...

Why???

thx,

Manuel

[Thomas Jakob]

Re: Another problem with singleton...

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Manuel wrote:[color=blue]
> This is the singleton I'm trying to write:
>
> global.h
> ----------------------------------------
> class Global
> {
> int i;
> static Global glob;
> //Global(int x): i(x) { } ;
> Global();
> Global& operator=(Globa l&); // Disallowed
> Global(const Global&); // Disallowed
>
> //some global variables
> int myVar;
>
> public:
> static Global& instance() { return glob; }
>
> //some set variables
> void setmyVar(int);
>
> //some get functions
> int getmyVar();
>
> };
> -----------------------------------------[/color]

<snip>

Here you declare a constructor Global::Global( ). It will be called to
instance the static member 'glob', but you haven't defined it.



- --
Greetings, Thomas Jakob
quicix (at) gmail (dot) com
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[Manuel]

Re: Another problem with singleton...

Thomas Jakob wrote:
[color=blue]
>
> Here you declare a constructor Global::Global( ). It will be called to
> instance the static member 'glob', but you haven't defined it.[/color]

To make the experiment I've defined it in header file:

------------------------------------
class Global
{
int i;
static Global glob;
//Global(int x): i(x) { } ;
Global();
Global& operator=(Globa l&); // Disallowed
Global(const Global&); // Disallowed

//some global variables
int myVar;

public:
static Global& instance() { return glob; }

//some set variables
void setmyVar(int);

//some get functions
int getmyVar();

};

Global::Global( ){};
-------------------------------------

calling it in main code with:

Global Global::glob;

the compiler return various errors (global.cpp was the same as previous
post):

global.o(.text+ 0x0):global.cpp : multiple definition of `Global::Global ()'
main.o(.text+0x 168):main.cpp: first defined here
global.o(.text+ 0x6):global.cpp : multiple definition of `Global::Global ()'
main.o(.text+0x 16e):main.cpp: first defined here
collect2: ld returned 1 exit status

Where is the error :-( ??

[Manuel]

Re: Another problem with singleton...

Manuel wrote:
[color=blue]
> calling it in main code with:
>
> Global Global::glob;
>
> the compiler return various errors (global.cpp was the same as previous
> post):
>
> global.o(.text+ 0x0):global.cpp : multiple definition of `Global::Global ()'
> main.o(.text+0x 168):main.cpp: first defined here
> global.o(.text+ 0x6):global.cpp : multiple definition of `Global::Global ()'
> main.o(.text+0x 16e):main.cpp: first defined here
> collect2: ld returned 1 exit status
>
> Where is the error :-( ??[/color]


Please, help!!!

[Rennie deGraaf]

Re: Another problem with singleton...

Manuel wrote:[color=blue]
> Thomas Jakob wrote:
>[color=green]
>>
>> Here you declare a constructor Global::Global( ). It will be called to
>> instance the static member 'glob', but you haven't defined it.[/color]
>
>
> To make the experiment I've defined it in header file:
>
> ------------------------------------
> class Global
> {
> int i;
> static Global glob;
> //Global(int x): i(x) { } ;
> Global();
> Global& operator=(Globa l&); // Disallowed
> Global(const Global&); // Disallowed
>
> //some global variables
> int myVar;
>
> public:
> static Global& instance() { return glob; }
>
> //some set variables
> void setmyVar(int);
>
> //some get functions
> int getmyVar();
>
> };
>
> Global::Global( ){};[/color]

Is this line in the header file? If so, then it will be defined in
every .cpp file that includes the header. Try putting it in a .cpp file
instead, and see if that fixes anything.

Rennie deGraaf

[Manuel]

Re: Another problem with singleton...

Rennie deGraaf wrote:
[color=blue][color=green]
>>Global::Globa l(){};[/color]
>
>
> Is this line in the header file? If so, then it will be defined in
> every .cpp file that includes the header. Try putting it in a .cpp file
> instead, and see if that fixes anything.[/color]

It work. THANKS!

But there is another thing I dont understand.
If define into header is an error, why the code below work (in the
header file)?

Global::Global( ){};

It's a definition, and it's into header too...

thx,

Manuel

[Manuel]

Re: Another problem with singleton...

Manuel wrote:[color=blue]
> Rennie deGraaf wrote:
>[color=green][color=darkred]
>>> Global::Global( ){};[/color]
>>
>>
>>
>> Is this line in the header file? If so, then it will be defined in
>> every .cpp file that includes the header. Try putting it in a .cpp file
>> instead, and see if that fixes anything.[/color]
>
>
> It work. THANKS!
>
> But there is another thing I dont understand.
> If define into header is an error, why the code below work (in the
> header file)?
>
> Global::Global( ){};
>
> It's a definition, and it's into header too...
>[/color]

help!

[pavel.turbin@gmail.com]

Re: Another problem with singleton...

I think it is because you have declared, but not defined ctor
Global::Global( ) which is expected to create object Global
Global::glob;

You should define at least some constructor or remove its declaration.

--------------
class Global
{
int i;
static Global glob;
//Global(int x): i(x) { } ;
Global() // <----
{
i = 0;
}
----------

[Jim Langston]

Re: Another problem with singleton...


"Manuel" <manuelbastioni REMOVETHIS@tin. it> wrote in message
news:43c0efbc$0 $1076$4fafbaef@ reader1.news.ti n.it...[color=blue]
> Rennie deGraaf wrote:
>[color=green][color=darkred]
>>>Global::Glob al(){};[/color]
>>
>>
>> Is this line in the header file? If so, then it will be defined in
>> every .cpp file that includes the header. Try putting it in a .cpp file
>> instead, and see if that fixes anything.[/color]
>
> It work. THANKS!
>
> But there is another thing I dont understand.
> If define into header is an error, why the code below work (in the header
> file)?
>
> Global::Global( ){};
>
> It's a definition, and it's into header too...
>
> thx,
>
> Manuel[/color]

Because that's the way C++ works. It's allowed in the class definition (?
is it the definition? I think so).

[Shezan Baig]

Re: Another problem with singleton...

Manuel wrote:[color=blue]
> But there is another thing I dont understand.
> If define into header is an error, why the code below work (in the
> header file)?
>
> Global::Global( ){};[/color]


It will work only if it is included in 1 translation unit (i.e., from
within one cpp file). Otherwise you will need to make it inline. To
do that, check out this FAQ, and the one after it:

http://www.parashift.com/c++-faq-lite/inline-functions.html#faq-9.7

Hope this helps,
-shez-

[Shezan Baig]

Re: Another problem with singleton...

Manuel wrote:[color=blue]
> But there is another thing I dont understand.
> If define into header is an error, why the code below work (in the
> header file)?
>
> Global::Global( ){};[/color]


It will work only if it is included in 1 translation unit (i.e., from
within one cpp file). Otherwise you will need to make it inline. To
do that, check out this FAQ, and the one after it:

http://www.parashift.com/c++-faq-lite/inline-functions.html#faq-9.7

Hope this helps,
-shez-

[Thomas Tutone]

Re: Another problem with singleton...

Manuel wrote:[color=blue]
> Manuel wrote:[color=green]
> > Rennie deGraaf wrote:
> >[color=darkred]
> >>> Global::Global( ){};[/color][/color][/color]
[color=blue][color=green][color=darkred]
> >> Is this line in the header file? If so, then it will be defined in
> >> every .cpp file that includes the header. Try putting it in a .cpp file
> >> instead, and see if that fixes anything.[/color][/color][/color]
[color=blue][color=green]
> > It work. THANKS!
> >
> > But there is another thing I dont understand.
> > If define into header is an error, why the code below work (in the
> > header file)?
> >
> > Global::Global( ){};
> >
> > It's a definition, and it's into header too...
> >[/color]
>
> help![/color]

I suspect you will find that the following link will help you solve (or
get help solving) your problem:

http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.8

It's no longer clear what your problem is. You need to restate it in
full so that folks have an opportunity to understand what you are
asking.

Best regards,

Tom