Classes vs Structs?

[desktop]

There is a lot of info on this topic on google. But in Bjarne Stroustrup
's book page 225 he writes:

"The declaration of Date in the previous subsection (declared as a
struct) provides a set of functions for manipulating a Date. However, it
does not specify that those functions should be the only ones to depend
directly on Date ’s representation and the only ones to directly access
objects of class Date . This restriction
can be expressed by using a class instead of a struct"
But I don't see why you need a class for this, on page 234 he even shows
that you can have private and public fields and functions in a struct
also. Is it an error in the book that he writes that you need a class to
make data private?

[Zeppe]

desktop wrote:

There is a lot of info on this topic on google. But in Bjarne Stroustrup
's book page 225 he writes:

"The declaration of Date in the previous subsection (declared as a
struct) provides a set of functions for manipulating a Date. However, it
does not specify that those functions should be the only ones to depend
directly on Date ’s representation and the only ones to directly access
objects of class Date . This restriction
can be expressed by using a class instead of a struct"
But I don't see why you need a class for this, on page 234 he even shows
that you can have private and public fields and functions in a struct
also. Is it an error in the book that he writes that you need a class to
make data private?

no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword. Read
http://www.parashift.com/c++-faq-lit...s.html#faq-7.8

Regards,

Zeppe

[Anonymous]

On Jun 7, 1:55 pm, Zeppe
<zep_p@.remove. all.this.long.c omment.yahoo.it wrote:

desktop wrote:

There is a lot of info on this topic on google. But in Bjarne Stroustrup
's book page 225 he writes:

"The declaration of Date in the previous subsection (declared as a
struct) provides a set of functions for manipulating a Date. However, it
does not specify that those functions should be the only ones to depend
directly on Date 's representation and the only ones to directly access
objects of class Date . This restriction
can be expressed by using a class instead of a struct"

But I don't see why you need a class for this, on page 234 he even shows
that you can have private and public fields and functions in a struct
also. Is it an error in the book that he writes that you need a class to
make data private?

no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword. Readhttp://www.parashift.c om/c++-faq-lite/classes-and-objects.html#fa q-7.8

Regards,

Zeppe

There are certain things you got to decide by yourself while coding.
Now if you want to have you code in C++ but you want to use struct
that will depend upon the limits of struct. If there is something
struct can't handle then you got to use class.

Read this : http://carcino.gen.nz/tech/cpp/struct_vs_class.php

Regards,
ar

"There are things known and things unknown, in between are The Doors."

[Gavin Deane]

On 7 Jun, 11:05, Anonymous <ashwani.ra...@ gmail.comwrote:

There are certain things you got to decide by yourself while coding.
Now if you want to have you code in C++ but you want to use struct
that will depend upon the limits of struct. If there is something
struct can't handle then you got to use class.

What limits do you think struct has? What do you think struct can't
handle that class can?

Read this :http://carcino.gen.nz/tech/cpp/struct_vs_class.php

That link describes the near-equivalence of struct and class (although
where it talks of members it should talk of members and base classes -
see FAQ 7.8) and doesn't mention any "limit" or anything "struct can't
handle". It appears to contradict what you say above.

Gavin Deane

[Zeppe]

Anonymous wrote:

On Jun 7, 1:55 pm, Zeppe
<zep_p@.remove. all.this.long.c omment.yahoo.it wrote:

>no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword. Readhttp://www.parashift.c om/c++-faq-lite/classes-and-objects.html#fa q-7.8

Regards,

Zeppe

There are certain things you got to decide by yourself while coding.
Now if you want to have you code in C++ but you want to use struct
that will depend upon the limits of struct. If there is something
struct can't handle then you got to use class.

I have to admit I've not understood your sentence. If I want to have my
code in c++ (yes, we are in c.l.c++) but I want to use struct that will
depend upon the the limits of struct (well, if I use struct it's because
I need something that depends upon the limits of struct...)... yeah, so
what? And for the last sentence, a struct can handle all the things a
class can, as I said. The only difference is the default visibility of
the members.

Read this : http://carcino.gen.nz/tech/cpp/struct_vs_class.php

That says in a longish way the same that the article that I cited,
agrees with me and contradict what you says. And, on top of that, the OP
didn't have any doubt about the fact that a C++ struct behaves the same
as a c++ class, so I can't really understand the point of the post.

Regards,

Zeppe

Regards,
ar

"There are things known and things unknown, in between are The Doors."

[Gennaro Prota]

On Thu, 07 Jun 2007 09:55:14 +0100, Zeppe wrote:

>no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword.

In what language?

--
Gennaro Prota -- C++ Developer, For Hire
https://sourceforge.net/projects/breeze/
(replace 'address' with 'name.surname' to mail)

[desktop]

Anonymous wrote:

On Jun 7, 1:55 pm, Zeppe
<zep_p@.remove. all.this.long.c omment.yahoo.it wrote:

>desktop wrote:

>>There is a lot of info on this topic on google. But in Bjarne Stroustrup
's book page 225 he writes:
"The declaration of Date in the previous subsection (declared as a
struct) provides a set of functions for manipulating a Date. However, it
does not specify that those functions should be the only ones to depend
directly on Date 's representation and the only ones to directly access
objects of class Date . This restriction
can be expressed by using a class instead of a struct"
But I don't see why you need a class for this, on page 234 he even shows
that you can have private and public fields and functions in a struct
also. Is it an error in the book that he writes that you need a class to
make data private?

no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword. Readhttp://www.parashift.c om/c++-faq-lite/classes-and-objects.html#fa q-7.8

Regards,

Zeppe

There are certain things you got to decide by yourself while coding.
Now if you want to have you code in C++ but you want to use struct
that will depend upon the limits of struct. If there is something
struct can't handle then you got to use class.

Read this : http://carcino.gen.nz/tech/cpp/struct_vs_class.php

Regards,
ar

"There are things known and things unknown, in between are The Doors."

Ok so it seems that there is no difference between structs and classes
in C++ besides the visibility. But in this article:

http://blog.devstone.com/aaron/archi...06/27/205.aspx

the author mentions that structs are passed as value while classes are
passed as reference. So if I know that my struct/class will contain a
lot of data I would go for a class since all the content will not be
copied each time I pass it to a function.

He also describes that you cannot have a constructor without parameters
in a struct, but that seems to work fine, this compiles:

struct bigblop {
bigblop(){
a = 345;
}
int a;
int b;

int geta() {
return a;
}

void seta(int i) {
a= i;
}

};

[Zeppe]

Gennaro Prota wrote:

On Thu, 07 Jun 2007 09:55:14 +0100, Zeppe wrote:

>no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword.

In what language?

C++, what else? Just saying that defining classes with the struct
keyword is considered deprecated, and that usually the struct keyword is
used mostly for simple data structures. It's not formally deprecated,
but it's a bad habit, such as using macros and stuff like that.

Regards,

Zeppe

[=?windows-1252?q?Erik_Wikstr=F6m?=]

On 7 Juni, 13:17, desktop <[e-mail] ote:

Anonymous wrote:

On Jun 7, 1:55 pm, Zeppe
<zep_p@.remove. all.this.long.c omment.yahoo.it wrote:

desktop wrote:
There is a lot of info on this topic on google. But in Bjarne Stroustrup
's book page 225 he writes:
"The declaration of Date in the previous subsection (declared as a
struct) provides a set of functions for manipulating a Date. However,it
does not specify that those functions should be the only ones to depend
directly on Date 's representation and the only ones to directly access
objects of class Date . This restriction
can be expressed by using a class instead of a struct"
But I don't see why you need a class for this, on page 234 he even shows
that you can have private and public fields and functions in a struct
also. Is it an error in the book that he writes that you need a classto
make data private?
no, it's not an error. Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword. Readhttp://www.parashift.c om/c++-faq-lite/classes-and-objects.html#fa q-7.8

Regards,

Zeppe

There are certain things you got to decide by yourself while coding.
Now if you want to have you code in C++ but you want to use struct
that will depend upon the limits of struct. If there is something
struct can't handle then you got to use class.

Read this :http://carcino.gen.nz/tech/cpp/struct_vs_class.php

Regards,
ar

"There are things known and things unknown, in between are The Doors."

Ok so it seems that there is no difference between structs and classes
in C++ besides the visibility. But in this article:

http://blog.devstone.com/aaron/archi...06/27/205.aspx

the author mentions that structs are passed as value while classes are
passed as reference. So if I know that my struct/class will contain a
lot of data I would go for a class since all the content will not be
copied each time I pass it to a function.

The author is talking about Managed C++ (a predecessor to C++/CLR), in
which there was some rule like that. In C++/CLR you have to declare
the class *or* struct to be either of value- of ref-type. This however
is totally off-topic in here and (as others have pointed out) the only
difference between struc and class in C++ is the default visibility of
members.

--
Erik Wikström

[James Kanze]

On Jun 7, 10:55 am, Zeppe
<zep_p@.remove. all.this.long.c omment.yahoo.it wrote:

desktop wrote:

There is a lot of info on this topic on google. But in Bjarne Stroustrup
's book page 225 he writes:

"The declaration of Date in the previous subsection (declared as a
struct) provides a set of functions for manipulating a Date. However, it
does not specify that those functions should be the only ones to depend
directly on Date ?s representation and the only ones to directly access
objects of class Date . This restriction
can be expressed by using a class instead of a struct"

But I don't see why you need a class for this, on page 234 he even shows
that you can have private and public fields and functions in a struct
also. Is it an error in the book that he writes that you need a class to
make data private?

no, it's not an error.

It depends on how you interpret it. I'm pretty sure that in
this case, Stroustrup is comparing C-style structs to classes;
that by using a class, with everything that C++ supports in
classes, you can express this restriction, which you cannot in a
C style struct. It has nothing to do with the keyword used to
define the type.

Stroustrup doesn't say that you _need_ to create
a class. He says that you can solve that problem creating a class.
Actually, you can solve it also declaring the members private in a
struct. It's deprecated, anyway, such a use of the struct keyword.

Not at all. There's not been the slightest suggestion to
deprecate the keyword struct, at least to my knowledge. The
fact remains that both keywords are legal, and that in C++,
regardless of which keyword you use, you are defining a class.
As a matter of style, only, many people do make a distinction,
but the exact distinction tends to vary from one person to the
next.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
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