Question about objects

[R2D2]

Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

class Inherited : public Base{};

void foo(std::vector<Basearg) {}

void main() {
std::vector<Inheritedv1;
v1.push_back(Inherited());

// does work
std::vector<Basev2;
for(int i=0; i<v1.size(); v2.push_back(v1[i++]));
foo(v2);

// doesn't work
foo(v1);
}

[Default User]

R2D2 wrote:

Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

Because it's C++, and this is a C newsgroup.

Try comp.lang.c++. When you post it there, change the return type of
main() to int, and explain what you mean by "does not work".

Brian

[Pete Becker]

On 2007-08-28 19:13:17 -0400, "Default User" <de***********@yahoo.comsaid:

R2D2 wrote:

>Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

Because it's C++, and this is a C newsgroup.

For some unspecified value of "this". I don't read comp.lang.c, but I
do read comp.lang.c++, and that's where I'm reading this message.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[LR]

R2D2 wrote:

Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

class Inherited : public Base{};

Inherited is a kind of Base;
http://www.parashift.com/c++-faq-lit....html#faq-19.3

But

std::vector<Inheritedis not a std::vector<Base>
http://www.parashift.com/c++-faq-lit....html#faq-21.3

LR

[pete]

R2D2 wrote:

>
Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.

#include <vector>

class Base {};

class Inherited : public Base{};

void foo(std::vector<Basearg) {}

void main() {
std::vector<Inheritedv1;
v1.push_back(Inherited());

// does work
std::vector<Basev2;
for(int i=0; i<v1.size(); v2.push_back(v1[i++]));
foo(v2);

// doesn't work
foo(v1);
}

Not in comp.lang.c. No. Absolutely not.

Followup To: comp.lang.c++

--
pete

[CBFalconer]

R2D2 wrote:

>
could someone please explain to me, why in the
following code the second approach does not work?

#include <vector>

class Base {};

class Inherited : public Base{};

void foo(std::vector<Basearg) {}

void main() {
std::vector<Inheritedv1;
v1.push_back(Inherited());

// does work
std::vector<Basev2;
for(int i=0; i<v1.size(); v2.push_back(v1[i++]));
foo(v2);

// doesn't work
foo(v1);
}

This is C++, not C. F'ups set.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com

[Richard Heathfield]

Default User said:

R2D2 wrote:

>Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

Because it's C++,

Actually, it isn't...

and this is a C newsgroup.

....and this is /also/ a C++ newsgroup, thanks to a broken crosspost.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[CBFalconer]

Richard Heathfield wrote:

Default User said:

>R2D2 wrote:

>>>
could someone please explain to me, why in the
following code the second approach does not work?

#include <vector>

class Base {};

Because it's C++,

Actually, it isn't...

>and this is a C newsgroup.

...and this is /also/ a C++ newsgroup, thanks to a broken crosspost.

It won't be, if people observe the F'up I have set.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com

[R2D2]

I don't really follow this - could you give a fuller explanation?

On 29 Aug 2007 at 0:01, LR wrote:

R2D2 wrote:

>Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

class Inherited : public Base{};

Inherited is a kind of Base;
http://www.parashift.com/c++-faq-lit....html#faq-19.3

But

std::vector<Inheritedis not a std::vector<Base>
http://www.parashift.com/c++-faq-lit....html#faq-21.3

LR

[R2D2]

I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

On 29 Aug 2007 at 8:55, CBFalconer wrote:

Richard Heathfield wrote:

>Default User said:

>>R2D2 wrote:

could someone please explain to me, why in the
following code the second approach does not work?

#include <vector>

class Base {};

Because it's C++,

Actually, it isn't...

>>and this is a C newsgroup.

...and this is /also/ a C++ newsgroup, thanks to a broken crosspost.

It won't be, if people observe the F'up I have set.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

[Default User]

R2D2 wrote:

I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

It doesn't belong here. There is NO underlying C code. There is C++
code that is compatible with C. People in comp.lang.c++ are perfectly
able to answer it.

You are off-topic in comp.lang.c, and you aren't going to get many good
answers.

Also:

Please don't top-post. Your replies belong following or interspersed
with properly trimmed quotes. See the majority of other posts in the
newsgroup, or:
<http://www.caliburn.nl/topposting.html>


Brian

[Francine.Neary]

On Aug 29, 9:24 pm, R2D2 <[e-mail]:

I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

Please don't top-post.

I found plenty of problems with the "underlying C code":

<stdin>:1:18: vector: No such file or directory
<stdin>:3: error: syntax error before "Base"
<stdin>:3: error: syntax error before '{' token
<stdin>:3: warning: ISO C does not allow extra `;' outside of a
function
<stdin>:5: error: syntax error before "Inherited"
<stdin>:5: warning: ISO C does not allow extra `;' outside of a
function
<stdin>:7: error: syntax error before ':' token
<stdin>:9: warning: return type of `main' is not `int'
<stdin>: In function `main':
<stdin>:10: error: syntax error before ':' token
<stdin>:11: error: `v1' undeclared (first use in this function)
<stdin>:11: error: (Each undeclared identifier is reported only once
<stdin>:11: error: for each function it appears in.)
<stdin>:11: warning: implicit declaration of function `Inherited'
<stdin>:13: error: syntax error before '/' token
<stdin>:15: error: `for' loop initial declaration used outside C99
mode
<stdin>:15: error: `v2' undeclared (first use in this function)
<stdin>:18: error: syntax error before '/' token
<stdin>:18:11: missing terminating ' character
<stdin>:18:11: warning: character constant too long for its type
<stdin>:10: warning: label `std' defined but not used

On 29 Aug 2007 at 8:55, CBFalconer wrote:

Richard Heathfield wrote:

Default User said:
R2D2 wrote:

>>could someone please explain to me, why in the
following code the second approach does not work?

>>#include <vector>

>>class Base {};

>Because it's C++,

Actually, it isn't...

>and this is a C newsgroup.

...and this is /also/ a C++ newsgroup, thanks to a broken crosspost.

It won't be, if people observe the F'up I have set.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

[J. J. Farrell]

On Aug 29, 9:24 pm, R2D2 <[e-mail]:

I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

What on earth are you talking about? What do you mean by "underlying C
code"? No-one in comp.lang.c can usefully comment if your post is not
about C, and there was nothing even vaguely related to C in your post.

[LR]

R2D2 wrote:

Your top posting has been moved. This will not be posted in comp.lang.c.

On 29 Aug 2007 at 0:01, LR wrote:

>R2D2 wrote:

>>Hi,

could someone please explain to me, why in the
following code the second approach does not work?

Thanks for your help.
#include <vector>

class Base {};

class Inherited : public Base{};

Inherited is a kind of Base;
http://www.parashift.com/c++-faq-lit....html#faq-19.3

But

std::vector<Inheritedis not a std::vector<Base>
http://www.parashift.com/c++-faq-lit....html#faq-21.3

I don't really follow this - could you give a fuller explanation?

I'll take a stab at it, but I suggest that you read the faq and ask a
more specific question.

Also, please don't post your follow up to comp.lang.c. This doesn't
belong there.
Below, Inherited is a child class of Base and inherits from Base.
X<Inheritedis not a child class of X<Baseand does not inherit from
X<Base>

Compare this with Y<Inheritedand Y<Basebelow.
class Base {
public:
virtual ~Base() {}
};

class Inherited : public Base {};

template<typename T>
class X {};

template<typename T>
class Y : public Base {}

int main() {

// ok
Inherited i;
Base *pb = &i;
Base &b = i;
X<Inheritedxi;
X<Base*pxb = &xi; // not ok, won't compile
X<Base&xb = xi; // not ok, won't compile

// ugly, but both Y<Inheritedand Y<Base>
// inherit from Base
// It's just an example.
Y<Inheritedyi;
Y<Baseyb;
Base &pyi = yi;
Base &pyb = yb;
}

LR

[R2D2]

Do you understand what C++ is? It's the C language, with a few
extensions bolted on like objects and polymorphism. So in any
malfunctioning code, the problem might be the C base code, or the C++
extension parts. So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

On 29 Aug 2007 at 20:37, J. J. Farrell wrote:

On Aug 29, 9:24 pm, R2D2 <[e-mail]:

>I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

What on earth are you talking about? What do you mean by "underlying C
code"? No-one in comp.lang.c can usefully comment if your post is not
about C, and there was nothing even vaguely related to C in your post.

[=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?=]

On 2007-08-30 00:17, R2D2 wrote:

On 29 Aug 2007 at 20:37, J. J. Farrell wrote:

>On Aug 29, 9:24 pm, R2D2 <[e-mail]:

>>I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

What on earth are you talking about? What do you mean by "underlying C
code"? No-one in comp.lang.c can usefully comment if your post is not
about C, and there was nothing even vaguely related to C in your post.

Do you understand what C++ is? It's the C language, with a few
extensions bolted on like objects and polymorphism. So in any
malfunctioning code, the problem might be the C base code, or the C++
extension parts. So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

Please don't top-post, see the FAQ, section 5, for more information
about how to format your replies.
http://www.parashift.com/c++-faq-lite/how-to-post.html

His understanding of what C++ is is better than yours. While what you
said was true once upon a time this is no longer the case. When BS
created C++ it started out as an extension to the C language, but since
then both languages have evolved, and not always in the same direction.
The result of this evolution is that there are now lots of valid C++
code that is also valid C code, however there is an ever greater amount
of C++ code that is *not* valid C. Likewise there are now lots of valid
C code that is also valid C++, and also much valid C that is *not* valid
C++.

An it's not just the classes and templates, there is code that is both
valid C and valid C++ that does not have the exact same meaning, which
can cause a lot of problems.

More to the point, of the code you posted in the original message not a
single line would have compiles or been meaningful in C, but in C++
there was only one slight error (except for the problem your question
was about).

--
Erik Wikström

[Old Wolf]

On Aug 30, 10:17 am, R2D2 <[e-mail]:

Do you understand what C++ is? It's the C language, with a few
extensions bolted on like objects and polymorphism.

Not true (and off-topic to discuss)

So in any malfunctioning code, the problem might be the
C base code, or the C++ extension parts.

Please post just the "C base code" parts of your program.
Then we can tell you if anything is wrong with that part.

So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

Well, C++ is just Java with a few libraries missing and
slightly altered syntax. Why not ask in comp.lang.java too?

[Keith Thompson]

R2D2 <r2**@spamtrap.invalidwrites:

Do you understand what C++ is? It's the C language, with a few
extensions bolted on like objects and polymorphism. So in any
malfunctioning code, the problem might be the C base code, or the C++
extension parts. So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

Most of us here understand what C++ is better than you do.

C and C++ are two distinct languages. C++ happens to contain most of
the features of C as a subset, but those features are *part of C++*.
If I write
int x = 42;
it could be valid C or valid C++. If I write it as part of a C++
program, it's C++, and the folks in comp.lang.c++ are perfectly
competent to discuss it. They don't need to run to the C experts to
ask about features of their own language.

And again, please stop top-posting. Read the following:

http://www.caliburn.nl/topposting.html
http://www.cpax.org.uk/prg/writings/topposting.php

I've redirected followups to comp.lang.c++, where this entire thread
should have been in the first place.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Old Wolf]

On Aug 30, 8:23 am, R2D2 <[e-mail]:

I don't really follow this - could you give a fuller explanation?

"This artoo unit is malfunctioning. Top-post switch
is stuck in the 'on' position. Request assistance."

[Default User]

R2D2 wrote:

Do you understand what C++ is? It's the C language, with a few
extensions bolted on like objects and polymorphism. So in any
malfunctioning code, the problem might be the C base code, or the C++
extension parts. So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

*plonk*

Brian

[pete]

R2D2 wrote:

>
I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

OK.
Here's what's wrong with your program
from a C point of view:
There isn't any part of your program
that means anything in C.

--
pete

[Default User]

Old Wolf wrote:

On Aug 30, 8:23 am, R2D2 <[e-mail]:

I don't really follow this - could you give a fuller explanation?

"This artoo unit is malfunctioning. Top-post switch
is stuck in the 'on' position. Request assistance."

Scrap it.


Brian

[Old Wolf]

On Aug 29, 10:59 am, R2D2 <[e-mail]:

could someone please explain to me, why in the
following code the second approach does not work?

class Base {};
class Inherited : public Base{};
void foo(std::vector<Basearg) {}

void main() {

Should be:
int main() {

std::vector<Inheritedv1;

// doesn't work
foo(v1);

There is no implicit conversion from vector<Inheritedto
vector<Base>.

[Flash Gordon]

R2D2 wrote, On 29/08/07 23:17:

Do you understand what C++ is?

Lots of people here do. It is a language.

It's the C language, with a few
extensions bolted on like objects and polymorphism.

No, it is a different language. A number of things that are legal C are
illegal C++.

So in any
malfunctioning code, the problem might be the C base code, or the C++
extension parts.

No, because there is no "C base code" only C++ code when you are writing
C++.

So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

What makes you think the people in comp.lang.c++ don't know all of the
"C base code?"

No, it is not reasonable to ask in comp.lang.c about C++ code, and since
you know about comp.lang.c++ you have no good excuse for doing so.

On 29 Aug 2007 at 20:37, J. J. Farrell wrote:

<snip>

Don't top post. Your reply belongs under or interspersed with the
message you are replying to.

Oh, and don't bother to reply. *PLONK*.
--
Flash Gordon

[CBFalconer]

R2D2 wrote: *** and top-posted - fixed ***

On 29 Aug 2007 at 0:01, LR wrote:

>R2D2 wrote:

>>>
could someone please explain to me, why in the
following code the second approach does not work?

#include <vector>

class Base {};

class Inherited : public Base{};

Inherited is a kind of Base;
http://www.parashift.com/c++-faq-lit....html#faq-19.3

But
std::vector<Inheritedis not a std::vector<Base>
http://www.parashift.com/c++-faq-lit....html#faq-21.3

I don't really follow this - could you give a fuller explanation?

It is not C. Please keep this out of c.l.c. F'ups set.

Please do not top-post. Your answer belongs after (or intermixed
with) the quoted material to which you reply, after snipping all
irrelevant material. I fixed this one. See the following links:

--
<http://www.catb.org/~esr/faqs/smart-questions.html>
<http://www.caliburn.nl/topposting.html>
<http://www.netmeister.org/news/learn2quote.html>
<http://cfaj.freeshell.org/google/ (taming google)
<http://members.fortunecity.com/nnqweb/ (newusers)

--
Posted via a free Usenet account from http://www.teranews.com

[BobR]

Why is it that you are asking people in this NG for something, but, when
they ask you for something (NOT to top-post), you throw mud in their face?

**plonk**

fool

[Pete Becker]

On 2007-08-29 19:09:49 -0400, pete <pf*****@mindspring.comsaid:

R2D2 wrote:

>>
I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

OK.
Here's what's wrong with your program
from a C point of view:
There isn't any part of your program
that means anything in C.

So why is this cross-posted to comp.lang.c++?

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Al Balmer]

On Thu, 30 Aug 2007 00:17:40 +0200 (CEST), R2D2
<r2**@spamtrap.invalidwrote:

>Do you understand what C++ is?

Yes. However, apparently you don't. Whatever you imagine to be the "C
base code" is surely understood by the experts who contribute to
c.l.c++.

And please stop top-posting.

It's the C language, with a few
extensions bolted on like objects and polymorphism. So in any
malfunctioning code, the problem might be the C base code, or the C++
extension parts. So it's perfectly suitable to ask in comp.lang.c as
well as comp.lang.c++.

On 29 Aug 2007 at 20:37, J. J. Farrell wrote:

>On Aug 29, 9:24 pm, R2D2 <[e-mail]:

>>I posted to comp.lang.c in case people could see a problem with the
underlying C code - please dont remove this crosspost. Thanks.

What on earth are you talking about? What do you mean by "underlying C
code"? No-one in comp.lang.c can usefully comment if your post is not
about C, and there was nothing even vaguely related to C in your post.

--
Al Balmer
Sun City, AZ