Newbie help using static variables

[Ramprasad A Padmanabhan]

Hi all,
I am a C & perl programmer trying my hand at c++. Can someone tell
whats wrong with this


--------------------------------------------------
using namespace std;
#include <iostream>

class Myobj {
public :
static int count;
Myobj(){
cout <<"Creating a new obj \n";
count++;
}
};

int main() {
Myobj *x,y;
x = new Myobj();
exit(0);
}

------------------------------------------------------------

My program does not compile on linux I get an error

g++ n4.cpp -o n4
/tmp/ccLKO0S2.o(.gnu.linkonce.t._ZN5MyobjC1Ev+0x1d): In function
`Myobj::Myobj[in-charge]()':
: undefined reference to `Myobj::count'
collect2: ld returned 1 exit status
make: *** [n4] Error 1


Thanks
Ram

 

[Sumit Rajan]

Hi all,
I am a C & perl programmer trying my hand at c++. Can someone tell
whats wrong with this


--------------------------------------------------
using namespace std;
#include <iostream>

class Myobj {
public :
static int count;
Myobj(){
cout <<"Creating a new obj \n";
count++;
}
};

You need to define count:

int Myobj::count = 0;

int main() {
Myobj *x,y;

Why not just:
Myobj x;

exit(0);

You may want to use return instead of exit.

}

------------------------------------------------------------

My program does not compile on linux I get an error

g++ n4.cpp -o n4
/tmp/ccLKO0S2.o(.gnu.linkonce.t._ZN5MyobjC1Ev+0x1d): In function
`Myobj::Myobj[in-charge]()':
: undefined reference to `Myobj::count'
collect2: ld returned 1 exit status
make: *** [n4] Error 1


Thanks
Ram

Regards,
Sumit.

 

[Tim Love]

Hi all,
I am a C & perl programmer trying my hand at c++. Can someone tell
whats wrong with this

Time to read the excellent FAQ. Start at
http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.10

 

[Brian Schelde]

You need to define count:

It is defined under public: static int count;

 

[matthias_k]

It is defined under public: static int count;

No, it's declared there. You also have to define it somewhere in a
compilation unit.

 

[Sumit Rajan]

It is defined under public: static int count;

That is a declaration of count; not a definition.

 

[Brian Schelde]

No, it's declared there. You also have to define it somewhere in a
compilation unit.

Oh yes, you are right of course.

 

[Brian Schelde]

That is a declaration of count; not a definition.

Yes. I got it the first time!