initializing private static members

[Madhav]

hi all,
I was trying the following code on the MS .net compiler:

class Item {
static int count;

public:
//static void init() { }

Item()
{
count++;
cout<<"construc ting Item"<<endl;
}
~Item()
{
count--;
cout<<"Destroyi ng Item #"<<count<<endl ;
}
};

The compiler kept giving me error for the unresloved symbol count.
After that , I made the variable count public and tried to assign 0 to
it in the main function. But still the same error was reported by the
compiler. I am confused about why the error has occured.

Thanks,
Madhav.

[Ian Collins]

Madhav wrote:

hi all,
I was trying the following code on the MS .net compiler:

class Item {
static int count;

public:
//static void init() { }

Item()
{
count++;
cout<<"construc ting Item"<<endl;
}
~Item()
{
count--;
cout<<"Destroyi ng Item #"<<count<<endl ;
}
};

The compiler kept giving me error for the unresloved symbol count.
After that , I made the variable count public and tried to assign 0 to
it in the main function. But still the same error was reported by the
compiler. I am confused about why the error has occured.

Do you have a definition of Item::count in a source file? Sounds like
you have forgotten to do this.

--
Ian Collins.

[luckyboy]

try to make initialization in this manner in your constructor:
Item() :count(0)
{
count++;
cout<<"construc ting Item"<<endl;
}

this manner is called the initializer list.
Note that you can't initialize constant members in a class by =
operator, instead you should use initializer list.
if there are many variables that you want to initialize feel free to
use comma, i.e.
Item():count1(o ), count2(3), count3(9)
{
count1++;
count2++;
count3++;
}

[Ian Collins]

luckyboy wrote:

try to make initialization in this manner in your constructor:
Item() :count(0)

No, this is wrong.

If you look back to the code you snipped, count is a static member. It
requires a definition.

--
Ian Collins.

[recover]

Yes, you must write " int Item::count=0; " in the source file (normal in
the .cpp file).

"Ian Collins" <ia******@hotma il.comwrite
news:4i******** ****@individual .net...

Madhav wrote:

hi all,
I was trying the following code on the MS .net compiler:

class Item {
static int count;

public:
//static void init() { }

Item()
{
count++;
cout<<"construc ting Item"<<endl;
}
~Item()
{
count--;
cout<<"Destroyi ng Item #"<<count<<endl ;
}
};

The compiler kept giving me error for the unresloved symbol count.
After that , I made the variable count public and tried to assign 0 to
it in the main function. But still the same error was reported by the
compiler. I am confused about why the error has occured.

Do you have a definition of Item::count in a source file? Sounds like
you have forgotten to do this.

--
Ian Collins.

[Ian Collins]

recover wrote:

Yes, you must write " int Item::count=0; " in the source file (normal in
the .cpp file).

Please don't top post!

"Ian Collins" <ia******@hotma il.comwrite
news:4i******** ****@individual .net...

>>Madhav wrote:

>>>hi all,
I was trying the following code on the MS .net compiler:

class Item {
static int count;

public:
//static void init() { }

Item()
{
count++;
cout<<"const ructing Item"<<endl;
}
~Item()
{
count--;
cout<<"Destr oying Item #"<<count<<endl ;
}
};

The compiler kept giving me error for the unresloved symbol count.
After that , I made the variable count public and tried to assign 0 to
it in the main function. But still the same error was reported by the
compiler. I am confused about why the error has occured.

Do you have a definition of Item::count in a source file? Sounds like
you have forgotten to do this.

--
Ian Collins.

--
Ian Collins.

[recover]

recover wrote:

Yes, you must write " int Item::count=0; " in the source file (normal

in

the .cpp file).

Please don't top post!

Thanks. I will be careful of.
I use Outlook Express to reply news. It's template take me to wite at begin
of letter.

[luckyboy]

Ian Collins wrote:

luckyboy wrote:

try to make initialization in this manner in your constructor:
Item() :count(0)

No, this is wrong.

If you look back to the code you snipped, count is a static member. It
requires a definition.

Thanx Ian Collins., this really helped me, but i wanna mention that i
still beginner in C++ field and just i wanna help others to solve their
problems. Again Thank you :)

[Madhav]

Ian Collins wrote:

luckyboy wrote:

try to make initialization in this manner in your constructor:
Item() :count(0)

No, this is wrong.

If you look back to the code you snipped, count is a static member. It
requires a definition.

--
Ian Collins.

hey Ian,
I wrote this in the main function by making the count
variable public:

int Item::count=0;

But now the compiler gives me something like:

error C2655: 'Item::count' : definition or redeclaration illegal in
current scope
see declaration of 'Item::count'

Then I moved the declaration above the main function and
everything worked fine. Can you please explain why it did not work in
previous case and works in this case?

I am not sure if the static variables follow the rules of
global variables for initialization. But I think this may just be it.

Regards,
Madhav.

[Ian Collins]

Madhav wrote:

Please try and keep some context, you should have replied to my first
posting.

>
hey Ian,
I wrote this in the main function by making the count
variable public:

int Item::count=0;

There's your mistake, the definition should be in the global scope (or
the same namespace as the class), not in main.

But now the compiler gives me something like:

error C2655: 'Item::count' : definition or redeclaration illegal in
current scope
see declaration of 'Item::count'

It's telling you you can't put the definition in main.

Then I moved the declaration above the main function and
everything worked fine. Can you please explain why it did not work in
previous case and works in this case?

I think I just have!

--
Ian Collins.