Declaration of a 'static' member data

[vib.cpp]

#include <iostream.h>

class Cat
{
public:
static HowManyCats;
private:
int itsage;
};

int Cat::HowManyCats=5;

int main()
{
cout<<"HowManyCats="<<Cat::HowManyCats<<endl;
}

The above is right, but the below is wrong, why cannot I declare
static data member in the class which it belong to?


#include <iostream.h>

class Cat
{
public:
static int HowManyCats;
private:
int itsage;
};

Cat::HowManyCats=5;

int main()
{
cout<<"HowManyCats="<<Cat::HowManyCats<<endl;
}


The following is still not true, why? can I declare the static member
inside the main function? And if I remove the int from the int
Cat::HowManyCats=5;statement, it passed the compile, but still blocked
when building, can anybody explain this for me?

#include <iostream.h>

class Cat
{
public:
static HowManyCats;
private:
int itsage;
};


int main()
{
int Cat::HowManyCats=5;
cout<<"HowManyCats="<<Cat::HowManyCats<<endl;

}

 

[Alf P. Steinbach]

* (e-mail address removed):

#include <iostream.h>

Note: this is a non-standard header. Some compilers lack this header. You should use

#include <iostream>

which is a standard header.

class Cat
{
public:
static HowManyCats;
private:
int itsage;
};

int Cat::HowManyCats=5;

int main()
{
cout<<"HowManyCats="<<Cat::HowManyCats<<endl;
}

The above is right, but the below is wrong, why cannot I declare
static data member in the class which it belong to?


#include <iostream.h>

class Cat
{
public:
static int HowManyCats;
private:
int itsage;
};

Cat::HowManyCats=5;

This definition lacks a type.

int main()
{
cout<<"HowManyCats="<<Cat::HowManyCats<<endl;
}


The following is still not true, why? can I declare the static member
inside the main function? And if I remove the int from the int
Cat::HowManyCats=5;statement, it passed the compile, but still blocked
when building, can anybody explain this for me?
#include <iostream.h>

class Cat
{
public:
static HowManyCats;
private:
int itsage;
};


int main()
{
int Cat::HowManyCats=5;
cout<<"HowManyCats="<<Cat::HowManyCats<<endl;

}

When you remove the 'int' in the code above you have an expression instead of a
declaration. An expression followed by a semicolon is a valid C++ statement. For
example,

42;

is a valid C++ statement where the value of the expression is discarded.

You should up your compiler's warning level so that it warns about statements
with no effect.

With g++ you can do that with '-Wall', with Visual C++ you can do that with '/W4'.

You get a link error because in this latest code there is no definition of
'Cat::HowManyCats'.

It has been declared but not defined.


Cheers & hth.,

- Alf

 

[Alf P. Steinbach]

* Alf P. Steinbach:

* (e-mail address removed):

Note: this is a non-standard header. Some compilers lack this header.
You should use

#include <iostream>

which is a standard header.



This definition lacks a type.



When you remove the 'int' in the code above you have an expression
instead of a declaration. An expression followed by a semicolon is a
valid C++ statement. For example,

42;

is a valid C++ statement where the value of the expression is discarded.

You should up your compiler's warning level so that it warns about
statements with no effect.

Note: the particular statement resulting from removing 'int' above has an effect
(it is an assignment). I didn't see that before hitting the Send button. But you
should up your compiler's warning level anyway. ;-)