class hate

[Amchi]

Alright .... this makes no sense ...

Declared a class 'diskStorage' in a header ...diskStorage. h
Defined it's contructor and methods ... in diskStorage.cpp

Included diskStorage header in a another class ...(server.h)
and then tried to declare a variable of type 'diskStorage' ...
like this ( inside server.h )

diskStorage local_disk;

this is what I get
"error: no matching function for call to `diskStorage::d iskStorage()"

Now, when I do this in the second class header file:
diskStorage* local_disk;

and then in the second class c o n t r u c t o r:
local_disk= new diskStorage(cyl inders,tracks,t rack_time);

it compiles and behaves....exce pt ...
calling local_disk->get_info() returns what it should o n l y in the
'server' class contructor.

when I call the local_disk->get_info() in a method that is part of
server class and not in it's constructor.... it returns garbage ...

I'm guessing the local_disk in the second case went out of scope.
But why does it not like me declaring a variable of type 'diskStorage'
in the first place?

Do I need to do this in the header file
diskStorage local_disk(); ////// would this not be a function !? and
not a variable

Dunno ...
Any ideas ?
---- server.h -----

#include "diskStorag e.h"

class server
{
private:
diskStorage local_disk; // should server not know what
diskStorage is ?
}
---- diskStorage.h-------
class diskStorage {
protected:
u_long _cylinder_count ;
u_long _sector_count;
u_long _track_time;
unsigned char geometry[12];

public:
//! class constructor
diskStorage(u_l ong cylinders,u_lon g sectors,u_long track_time);
~diskStorage();

void get_info();
};
--- diskStorage.cpp ----

#include "diskStorag e.h"

diskStorage::di skStorage(u_lon g cylinders, u_long sectors, u_long
track_time)
{
_cylinder_count = cylinders;
_sector_count = sectors;
_track_time = track_time;

cout<<"Cylinder s :"<< _cylinder_count <<endl;
cout<<"Sectors :" << _sector_count <<endl;
}
--- server.cpp---

server::server( u_long cylinders, u_long sectors, u_long track_time)
{
diskStorage local_disk(cyli nders,sectors,t rack_time);//this does not
work
local_disk = new diskStorage(cyl inders,sectors, track_time);//this does
work

}

I was sure I could declare a variable of any type in a header and
initialize it in elsewhere
Just like I can with any data type...but I seem to be wrong ...
Or just looked at the code for too long and missing something trivial.
These are of course just parts of the code but the rest is not relevant
and quite a mess.

The questions you may ask:
Q: Why am I separating class declarations and definitions?
A: 'Cause I hope to work on a project big enough (some day) where that
makes sense and am trying to get used to the idea.

Q: Why did I not look for examples ?
A: I did, but found nothing similar.

Q: Am I just trying to have someone else do my HW?
A: No, I need to learn b e f o r e someone asks me to do this (at
work).

btw. gdb tracing did not break where I told it to ... so now I'm
completely lost :-)

[David Harmon]

On 21 Nov 2006 17:19:05 -0800 in comp.lang.c++, "Amchi"
<am*********@gm ail.comwrote,

>diskStorage local_disk;

this is what I get
"error: no matching function for call to `diskStorage::d iskStorage()"

diskstorage has no constructor that takes no arguments (also known as a
'default' constructor.) For a simple diskstorage variable as written,
you must supply arguments for initialization.

diskStorage local_disk(cyli nders,tracks,tr ack_time);

>Do I need to do this in the header file
diskStorage local_disk(); ////// would this not be a function !? and
not a variable

You're right, that's a function.

The class member is:

diskStorage local_disk;

It's initialized in the constructor initialization list as

server::server( u_long cylinders, u_long sectors, u_long track_time)
: local_disk(cyli nders,sectors,t rack_time)
{
...

This issue is covered in Marshall Cline's C++ FAQ. See the topic
"[10.6] Should my constructors use "initializa tion lists" or
"assignment "?" It is always good to check the FAQ before posting.
You can read the FAQ at:
http://www.parashift.com/c++-faq-lite/

[Amchi]

Thank you.
Worked around it by changing the constructor to be empty and defined a
'mutator' method.

I appreciate you taking time to help.
Thanks again.
David Harmon wrote:

On 21 Nov 2006 17:19:05 -0800 in comp.lang.c++, "Amchi"
<am*********@gm ail.comwrote,

diskStorage local_disk;

this is what I get
"error: no matching function for call to `diskStorage::d iskStorage()"

diskstorage has no constructor that takes no arguments (also known as a
'default' constructor.) For a simple diskstorage variable as written,
you must supply arguments for initialization.

diskStorage local_disk(cyli nders,tracks,tr ack_time);

Do I need to do this in the header file
diskStorage local_disk(); ////// would this not be a function !? and
not a variable

You're right, that's a function.

The class member is:

diskStorage local_disk;

It's initialized in the constructor initialization list as

server::server( u_long cylinders, u_long sectors, u_long track_time)
: local_disk(cyli nders,sectors,t rack_time)
{
...

This issue is covered in Marshall Cline's C++ FAQ. See the topic
"[10.6] Should my constructors use "initializa tion lists" or
"assignment "?" It is always good to check the FAQ before posting.
You can read the FAQ at:
http://www.parashift.com/c++-faq-lite/

[eriwik]

On 22 Nov, 04:23, "Amchi" <amer.ter...@gm ail.comwrote:

Thank you.
Worked around it by changing the constructor to be empty and defined a
'mutator' method.

I'd like to point out (if you did not already know) that you can have
two (or more) constructors, one that takes no arguments, and one that
does. So you could keep your constructor and just create a new one that
creates a diskStorage with some default values.

PS. Next time, write your reply below that which you are replying to.
People get annoyed if you don't.

--
Erik Wikström

[Amchi]

er****@student. chalmers.se wrote:

On 22 Nov, 04:23, "Amchi" <amer.ter...@gm ail.comwrote:

Thank you.
Worked around it by changing the constructor to be empty and defined a
'mutator' method.

I'd like to point out (if you did not already know) that you can have
two (or more) constructors, one that takes no arguments, and one that
does. So you could keep your constructor and just create a new one that
creates a diskStorage with some default values.

Had a nightmare about it and in the middle of the night realized I
could have done that.
Stepping back and forgetting about it for a moment would have helped.

PS. Next time, write your reply below that which you are replying to.
People get annoyed if you don't.

Ok. My bad.

[Frederick Gotham]

---- server.h -----

#include "diskStorag e.h"

class server
{
private:
diskStorage local_disk; // should server not know what
diskStorage is ?
}

I don't know if you've omitted them because you're posting to a newsgroup,
but you should have inclusion guards in header files:

#ifndef INC_SERVER_HPP
#define INC_SERVER_HPP

/* Contents of Header file */

#endif

By the way, I advocate the "hpp" extension for C++ header files, an "h" for
C header files. (Same goes for "cpp" and "c").

---- diskStorage.h-------
class diskStorage {
protected:
u_long _cylinder_count ;
u_long _sector_count;
u_long _track_time;
unsigned char geometry[12];

public:
//! class constructor
diskStorage(u_l ong cylinders,u_lon g sectors,u_long track_time);
~diskStorage();

void get_info();
};

--- diskStorage.cpp ----

#include "diskStorag e.h"

diskStorage::di skStorage(u_lon g cylinders, u_long sectors, u_long
track_time)
{
_cylinder_count = cylinders;
_sector_count = sectors;
_track_time = track_time;

cout<<"Cylinder s :"<< _cylinder_count <<endl;
cout<<"Sectors :" << _sector_count <<endl;
}

You might prefer use of an "constructo r initialiser list" here. If you
don't know what that is, Google for it.

--

Frederick Gotham

[Jan Bornschlegel]

Frederick Gotham schrieb:

>---- server.h -----

#include "diskStorag e.h"

class server
{
private:
diskStorage local_disk; // should server not know what
diskStorage is ?
}

I don't know if you've omitted them because you're posting to a newsgroup,
but you should have inclusion guards in header files:

#ifndef INC_SERVER_HPP
#define INC_SERVER_HPP

/* Contents of Header file */

#endif

By the way, I advocate the "hpp" extension for C++ header files, an "h" for
C header files. (Same goes for "cpp" and "c").

Yes, this is absolutely wise.
By the way, to add some confusion to a C++ learner, let me add that in
the above case (in "server.h") you could (and imho should) use a class
forward declaration. If a class name is used only as parameter or return
value or member it is not necessary to include the header, it's ok to
add a line
class diskStorage;
and the compiler is perfectly happy. Try it ;)
Some of my colleagues swear that this makes loading time shorter, but I
never noticed that - maybe my projects were too few files....

Jan

[red floyd]

Jan Bornschlegel wrote:

Frederick Gotham schrieb:

>>---- server.h -----

#include "diskStorag e.h"

class server
{
private:
diskStorage local_disk; // should server not know what
diskStorage is ?
}

I don't know if you've omitted them because you're posting to a
newsgroup, but you should have inclusion guards in header files:

#ifndef INC_SERVER_HPP
#define INC_SERVER_HPP

/* Contents of Header file */

#endif

By the way, I advocate the "hpp" extension for C++ header files, an
"h" for C header files. (Same goes for "cpp" and "c").

Yes, this is absolutely wise.
By the way, to add some confusion to a C++ learner, let me add that in
the above case (in "server.h") you could (and imho should) use a class
forward declaration. If a class name is used only as parameter or return
value or member it is not necessary to include the header, it's ok to
add a line

Not quite true. If it's used as a param, return value, or *pointer or
reference* member, it's not necessary to include the header. If it's
used as a regular member, it is necessary. Otherwise, how would the
compiler know how much memory to allocate for (in the example) the servr
class?

[Earl Purple]

Frederick Gotham wrote:

By the way, I advocate the "hpp" extension for C++ header files, an "h" for
C header files. (Same goes for "cpp" and "c").

I use .hpp for exported headers, .hxx for private headers.

A private header is one that is not used outside of its module. (A
module here meaning a group of classes that implement functionality
that are reasonably well coupled together).

[Earl Purple]

Amchi wrote:

< snip down to the code >

>
---- server.h -----

#include "diskStorag e.h"

class server
{
private:
diskStorage local_disk; // should server not know what diskStorage is ?
}

I don't know at this point what diskStorage is or what server is but
this class hides nothing because anyone including server.h is
indirectly including diskStorage.h as well.

Better is generally to reduce the coupling by using a foward
declaration. This is often done with a "pImpl" class.

If using boost, one way here is to use scoped_ptr so:

class server
{
private:
boost::scoped_p tr< diskStorage local_disk;

// plus public interface, of course
};

You have to include the boost/scoped_ptr header to do this but you can
forwardly declare diskStorage here, including the header only in the
server.cpp.

Assuming that everyone is using boost regularly, it will not be
increasing the coupling by including the boost header.

If you do not want to add a dependency on boost for those using the
class (eg you are exporting it) then you can use a raw pointer, but you
have to manage it yourself (as well as managing copying and
assignment).

---- diskStorage.h-------
class diskStorage {
protected:
u_long _cylinder_count ;
u_long _sector_count;
u_long _track_time;
unsigned char geometry[12];

These should probably be private rather than protected. Magic numbers
(like 12) should normally be "enum"ed.

The questions you may ask:
Q: Why am I separating class declarations and definitions?
A: 'Cause I hope to work on a project big enough (some day) where that
makes sense and am trying to get used to the idea.

And also it's usually a sensible thing to do. The only main exceptions
are
1. when writing templates (because most compilers don't support export)
2. Writing something very generic that you want to be able to include
from multiple projects without having to link against anything
3. Writing a very trivial class, often a functor.

I also sometimes writing implementation classes with no header file at
all, and these are then sometimes exported as symbols but that's
another issue.