Variables & Headers Question

[homing]

Hey,

I have 2 simple Questions...

1 Question)

Where would you declare a local variable for a class?:

in the header?

class x{

private:
int y;

public:
};

or in the source file?

#include "x.h"

int y;

public X::X()
{
};

I'm always using the first one, also if it's an object:

class x{
private:
ClassY obj;
public:
 x();
};

X::X() : obj(new ClassY)
{
}

2 Question:

Where do you guys include headers, which you need for your class.
in the header file or source file?

At the moment, I Only include headers in the header if I already need them there.
Otherwise I put all includes in the source file.

[MikeyBoy]

1) This is really a design decision. Is the variable supposed to be part of the state of an instance of the class? Then it should be a non-static data member of the class, as in your first example.

The second example is defining a global variable, not a member of the class. Global variables should be avoided wherever possible.

2) As a general rule, you should reduce unnecessary coupling by including header files only where they are needed. So it sounds as though you're doing it right.

[JLBorges]

> Where would you declare a local variable for a class?

If it is an instance variable (one for each object instance), it has to be declared in the class as a non static member.

If it is a shared variable (common to all object instances),
either declare it as a static member of the class (and define it in the implementation file)
or define it as a non member with internal linkage in the implementation file.

Header:

struct account
{
    unsigned int number ; // instance variable
    // each instance of account has its own number, 
    // different accounts have different numbers.

    static const double rate_of_interest ; // static variable
    // all instances of account share a common rate of interest.
};

Implementation:
const double account::rate_of_interest = 8.3 ;


> At the moment, I Only include headers in the header if I already need them there.
> Otherwise I put all includes in the source file.

Yes, that is the way we do it too. As far as possible, we avoid gratuitous inclusion of one header in another header.