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Then why class were created?? struct itself is enough ..na?
nave
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but c++ structure can have visibility declarators (public, protected, private), and member functions too..
nave
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that's why i explicitely said C structs, not C++...
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toxcct wrote: that's why i explicitely said C structs, not C++...
So you deliberatly set him on a wrong track? 
Not very nice...
"We trained hard, but it seemed that every time we were beginning to form up into teams we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising: and a wonderful method it can be for creating the illusion of progress, while producing confusion, inefficiency and demoralisation."
-- Caius Petronius, Roman Consul, 66 A.D.
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toxcct wrote: are you stupid ?
No. Are you? 
toxcct wrote: C is a subset of C++, and you cannot do C++ hiding C totally
Absolutly totaly not.
Out modern C++ is derived from a old version of K&R-C by people with a deep understanding of and a great liking for C.
But C is in no way a subset of C++.
In many cases C++ can be considered a superset of C, but not in all.
And IMHO you really *should* not know too much of C to write good style C++.
toxcct wrote: C structs are different from C++ structs
Yes.
But C-structs were not what we others were talking about, and you were introducing them in a way carefully crafted as to not draw the attention.
"We trained hard, but it seemed that every time we were beginning to form up into teams we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising: and a wonderful method it can be for creating the illusion of progress, while producing confusion, inefficiency and demoralisation."
-- Caius Petronius, Roman Consul, 66 A.D.
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jhwurmbach wrote: is in no way a subset of C++.
yes it is. Read Bjarne Stroustrup about this.
jhwurmbach wrote: And IMHO you really *should* not know too much of C to write good style C++.
agreed, and i never said the opposite.
jhwurmbach wrote: C-structs were not what we others were talking about
i only talked about them because only introduced their purpose into the C++ language : compatibility
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jhwurmbach wrote: Out modern C++ is derived from a old version of K&R-C...
More specifically, it is a superset of ANSI C, which is, in turn, a superset of K&R C.
"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank
"Judge not by the eye but by the heart." - Native American Proverb
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DavidCrow wrote:
[Our modern C++] is a superset of ANSI C, which is, in turn, a superset of K&R C.
Hmm, really?!?
I was under the impression that the C++-Standard predates ANSI-C.
But i am much too lethargic to double-check that. 
"We trained hard, but it seemed that every time we were beginning to form up into teams we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising: and a wonderful method it can be for creating the illusion of progress, while producing confusion, inefficiency and demoralisation."
-- Caius Petronius, Roman Consul, 66 A.D.
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jhwurmbach wrote: I was under the impression that the C++-Standard predates ANSI-C.
I think they are roughly nine years apart. The ANSI C standard was completed in 1989. The ANSI-ISO C++ standard was completed in 1998. The next C++ standard is expected out within the next 3 years.
"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank
"Judge not by the eye but by the heart." - Native American Proverb
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DavidCrow wrote: The ANSI C standard was completed in 1989. The ANSI-ISO C++ standard was completed in 1998.
Yes, you are right.
I was thinking of ANSI-C99, but before there was a ANSI-C90.
DavidCrow wrote: The next C++ standard is expected out within the next 3 years.
That is what they are telling us for years.
I would guess that C++0X will need a hexadecimal digit for X...
"We trained hard, but it seemed that every time we were beginning to form up into teams we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising: and a wonderful method it can be for creating the illusion of progress, while producing confusion, inefficiency and demoralisation."
-- Caius Petronius, Roman Consul, 66 A.D.
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Hi guys,
havent found the answer for my question till now..discussion seems to be nice and interesting but pls answer to the question that i have asked..
thanks
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Your question has been answered quite a few times, additionally, a lot of links have been given.
Short recapitulation:
In classes, the default visibility is private, in structs, it is public.
Classes can be template parameters, where structs can not.
Thats all, folks.
-- modified at 8:11 Wednesday 9th August, 2006
"We trained hard, but it seemed that every time we were beginning to form up into teams we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising: and a wonderful method it can be for creating the illusion of progress, while producing confusion, inefficiency and demoralisation."
-- Caius Petronius, Roman Consul, 66 A.D.
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toxcct wrote: C is a subset of C++...
Maybe at a high level, but not in a pure mathematical sense. It's possible to have a valid C program that is not valid C++ code. C++ can be considered a superset of C, however.
"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank
"Judge not by the eye but by the heart." - Native American Proverb
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'class' is proper OO terminology, 'struct' isn't.
but default member access isn't the only difference between struct and class: you can't use templates on structs - only on classes .
a 'class' is intended to be the primary object type. 'struct' is for backwards compatibility. and, yes they overlap .
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Chris Losinger wrote: you can't use templates on structs - only on classes .
If you mean you can't use struct keyword inside of a template declaration, you are right. However, it is perfectly possible to make struct templates.
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right.
template < struct T > class nope {...}; = bad
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Default inheritance type: a struct entails public inheritance by default whereas a class entails private inheritance.
Regards
Amar
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Subramaniam s.V. wrote:
Can anybody tell me the exact "Difference between C++ Structures and C++ Classes".
This is discussed in The Design and Evolution of C++.
"Money talks. When my money starts to talk, I get a bill to shut it up." - Frank
"Judge not by the eye but by the heart." - Native American Proverb
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About differences. The default protection in case of class is "private", whereas in case of struct it is "public":
class A
{
int a;
. . .
};
struct A
{
int a;
. . .
};
The default inheritance protection in case of class is "private", whereas in case of struct it is "public":
class B : A
{
};
struct B : A
{
};
That’s my opinion about differences.
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struct and class in C++ are identical with the exception of their default visibility (private for class, public for struct). The struct keyword was a leftover from the C lineage of C++. That said, when a C++ compiler sees the struct keyword, it will compile it, but not in the same way that a C compiler would have. The C++ compiler will generate a default constructor, destructor, and copy-assignment operator (whereas a C compiler would just treat it as a new datatype).
They both exist in C++ because of the desire to be able to compile C code with a C++ compiler. Removing keywords such as this would have made such backwards-compatability impossible without first modifying the codebase.
If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week
Zac
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I'm putting together code for a template that implements some special tasks that I need and I want it to use with different CWnd based classes as template argument and ancestor at the same time like this:
template < class BASE >
class CLASS : public BASE
{
.
.
.
};
If I want to use it with CFormView and CDialog in the same project I need template argument dependent compiling, 'cause for example if I need to implement OnInitDialog() for CDialog, I must ignore it with CFormView, otherwise I get an error that this function is not the member of the base class.
I thought of doing string comparison of the BASE argument at the right places, but I'm not too familiar with macros.
#define STR_COMP(_base, _class) \
(strcmp(#_base, _class)==0)
and use it as
#if STR_COMP(BASE, "CDialog")
.....
#else if ...
....
#else
...
#endif
Of course it doesn't work....
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Maybe you should try a "specialization" of template classes? I suppose it may look like this:
template< class BASE >
class COMMON : public BASE
{
. . .
};
template< class BASE >
class CLASS : public COMMON< BASE >
{
};
template< >
class CLASS< CDialog > : public COMMON< CDialog >
{
. . .
};
template< >
class CLASS< CFormView > : public COMMON< CFormView >
{
. . .
};
Usage:
CLASS< CDialog > dlg;
CLASS< CFormView > form;
I hope this works.
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