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=(Global&); // 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::setmyVar(int i){myVar = i;}

//Get functions
int Global::getmyVar(){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::instance();
--------------------------------------------

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::instance();

it work...

Why???

thx,

Manuel

[Thomas Jakob]

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Hash: SHA1

Manuel wrote:

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=(Global&); // 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();

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

<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]

Thomas Jakob wrote:

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

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=(Global&); // 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+0x168):main.cpp: first defined here
global.o(.text+0x6):global.cpp: multiple definition of `Global::Global()'
main.o(.text+0x16e):main.cpp: first defined here
collect2: ld returned 1 exit status

Where is the error :-( ??

[Manuel]

Manuel wrote:

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+0x168):main.cpp: first defined here
global.o(.text+0x6):global.cpp: multiple definition of `Global::Global()'
main.o(.text+0x16e):main.cpp: first defined here
collect2: ld returned 1 exit status

Where is the error :-( ??

Please, help!!!

[Rennie deGraaf]

Manuel wrote:

Thomas Jakob wrote:

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

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=(Global&); // 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(){};

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]

Rennie deGraaf wrote:

Global::Global(){};

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.

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]

Manuel wrote:

Rennie deGraaf wrote:

Global::Global(){};

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.

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...

help!

[pavel.turbin]

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]

"Manuel" <ma**********************@tin.it> wrote in message
news:43**********************@reader1.news.tin.it. ..

Rennie deGraaf wrote:

Global::Global(){};

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.

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

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

[Shezan Baig]

Manuel wrote:

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 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-lit...s.html#faq-9.7

Hope this helps,
-shez-

[Shezan Baig]

Manuel wrote:

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 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-lit...s.html#faq-9.7

Hope this helps,
-shez-

[Thomas Tutone]

Manuel wrote:

Manuel wrote:

Rennie deGraaf wrote:

Global::Global(){}; 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.

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...

help!

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-lit...t.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