Why we need classes

[Pratts]

I am a new one who have joined u plz try to help me bcoz i could not
find ny sutiable answer foer this Question
Qus>>why do we need classes when structures provide similar
functionality??

[Kelly Mandrake]

structures are public by default and classes are private by default.
Unless you use the keywords private, public or protected, any member
funtions or member data in a structure will be public. The idea behind
encapsulation is to hide the details, it is desireable to make private
data and provide public interface methods that the user of the class
can use.

[Jack Klein]

On 27 Feb 2005 19:34:41 -0800, "Pratts" <it*********@re diffmail.com>
wrote in comp.lang.c++:

I am a new one who have joined u plz try to help me bcoz i could not
find ny sutiable answer foer this Question
Qus>>why do we need classes when structures provide similar
functionality??

A better way to ask this question would be:

"Why do we need structs in C++ when we have classes?"

There is a difference in default access, but this is really trivial.

Structs are needed for backwards compatibility with C code, of which
there were millions of lines in existence as C++ came into being.
Classes are little more than a documentation mechanism.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[osmium]

"Pratts" writes:

I am a new one who have joined u plz try to help me bcoz i could not
find ny sutiable answer foer this Question
Qus>>why do we need classes when structures provide similar
functionality??

If you mean why do we need the keyword "class" in addition to stuct, the
answer is, we don't. It's just for convenience and, as typically used,
improves documentation.

[DHOLLINGSWORTH2]

"Pratts" <it*********@re diffmail.com> wrote in message
news:11******** **************@ o13g2000cwo.goo glegroups.com.. .

I am a new one who have joined u plz try to help me bcoz i could not
find ny sutiable answer foer this Question
Qus>>why do we need classes when structures provide similar
functionality??

structures do not provide anywhere near the functionality you get from
classess.

Classess have constructors, that can be modified./overloaded.
Classes have destructors, that can be modified/ overloaded.
Classes allow for operator Overloads.
Classes have member functions, static functions.
Public, Private, and Protected Data and code.
Classes incapsulate. Structures Arrange.

The differences are vast. You will have to write some code to begin to
understand the impact.

I struggled with it for several months.

You gain Power, Robustness. A level of Protection, while increasing the
longevity of your code.

I can send you some examples done with both structures and class object, if
you'd like to see the difference.

dan
DH************* @cox.net

[440gtx]

> Classess have constructors, that can be modified./overloaded.

Classes have destructors, that can be modified/ overloaded.
Classes allow for operator Overloads.
Classes have member functions, static functions.
Public, Private, and Protected Data and code.
Classes incapsulate. Structures Arrange.

struct was upgraded in C++ and can do all of that too. Try it.

I personally stopped using the class keyword and went back to struct.
The reason is I can eliminate that silly "public:" statement at the
beginning needed to expose the constructor. In the end, "class" proved
to be just an unnecessary annoyance with no value add for me. I do use
public, protected, and private extensively to define structs.

[Martijn Mulder]

>> Classess have constructors, that can be

modified./overloaded. Classes have destructors, that can
be modified/ overloaded. Classes allow for operator
Overloads.
Classes have member functions, static functions.
Public, Private, and Protected Data and code.
Classes incapsulate. Structures Arrange.

struct was upgraded in C++ and can do all of that too.
Try it.

I personally stopped using the class keyword and went
back to struct. The reason is I can eliminate that silly
"public:" statement at the beginning needed to expose the
constructor. In the end, "class" proved to be just an
unnecessary annoyance with no value add for me. I do use
public, protected, and private extensively to define
structs.

Indeed. I think that 'class' and 'struct' where meant to be equivalent. I never
touched another class after reading what Bjarne Stroustrup wrote about it in the
Annotated C++ Reference Manual, Addison-Wesly Publishing Company, 1995,
Paragraph 11.2:

<quote>
(...) For example, novices often don't know about access specifiers and get
confused by this:

class X { public: f(); };
class Y : X { }; // no access specifier
// private by default

void g(Y* p)
{
p->f(); // error
}

Even experts can get caught. A compiler can be most helpful by issuing a warning
for the missing access specifier.
Having private as the default was chosen to reflect the general view that
things that are not explicitly declared public are private. Defining a default
access specifier was probably a mistake.
</quote>

He says that the default access specifier 'private' for classes was a mistake.
There should have been _no_ default access specifier, ie class should be
'public' by default, just like struct is. The difference between class and
struct is based on a mistake. A class was meant to act just like a struct does.

[Howard]

"Pratts" <it*********@re diffmail.com> wrote in message
news:11******** **************@ o13g2000cwo.goo glegroups.com.. .

I am a new one who have joined u plz try to help me bcoz i could not
find ny sutiable answer foer this Question
Qus>>why do we need classes when structures provide similar
functionality??

we r n nglsh lang nwsgrp her, not IM
try complt wrds nxt tm

[Pratts]

buddy very sorry to say that
u must go through the things again bcoz structures can do all that
constructor
destructors
operator Overloads and every thing that class can do
plz try this out
byEEEEEEEEEEE

[DHOLLINGSWORTH2]

"Pratts" <it*********@re diffmail.com> wrote in message
news:11******** **************@ l41g2000cwc.goo glegroups.com.. .

buddy very sorry to say that
u must go through the things again bcoz structures can do all that
constructor
destructors
operator Overloads and every thing that class can do
plz try this out
byEEEEEEEEEEE

Can structures have pure virtual Functions?
Can a structure prevent a programmer from erroneously ovewriting data
elements?
Can a structure have Private data?
Can a structure have Protected data?

The truth is I'm not sure, I use structs to set up Common data that the
Class objects will be using, and sharing with the outside world.