soft and program: comp.lang.c++ - 17 new messages in 14 topics

comp.lang.c++
http://groups.google.com/group/comp.lang.c++?hl=en

comp.lang.c++@googlegroups.com

Today's topics:

==============================================================================
TOPIC: OpenMP and functors
http://groups.google.com/group/comp.lang.c++/t/69a3ea80ba0eb730?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 2:42 pm
From: Robert Fendt

Hi all,

ok forget everything I said. I just forgot a 'private (j)'... shame on me. However, works now.

Regards,
Robert

==============================================================================
TOPIC: Classes named CFoo (was Re: Odd Exception Behavior)
http://groups.google.com/group/comp.lang.c++/t/ce3a580936f3cddd?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 2:43 pm
From: Jorgen Grahn

On Thu, 2010-02-04, none wrote:
> Alf P. Steinbach wrote:
...
>> * "C"-prefix for a class is a Microsoft-ism, therefore (almost
>> automatically)
>> ungood.
>
> Guilty as charged. I've been using the "C" prefix since the early days
> of Visual Studio.

More generally: I see this class CFoo scheme in a lot of postings
here. Why do people use it, *really*?

Microsoft may have had some reason to use it back in the 1980s or so,
before namespaces, before C++ was widely adopted, before their
programmers knew the language well, and they may have to keep it for
backwards-compatible reasons.

But that doesn't imply that *everyone else* has to use it, in their
own code, for new classes, in 2010. It provides no information and is
just in the way.

Are there broken tools in Microsoft-land which require it?
Misinformation in popular books? What?

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

==============================================================================
TOPIC: Incomplete types and std::vector
http://groups.google.com/group/comp.lang.c++/t/b0741c38fc15b5f7?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 2:58 pm
From: Stephen Howe

> I think that the point is that using std::auto_ptr in the pimpl idiom
>doesn't save much work. You still need to write an explicit destructor
>(and possibly constructor) and forbid copying and assignment of the
>class. Basically you are more or less simply changing a "delete data;"
>in the destructor to a "std::auto_ptr" in the class declaration. Not
>much of a saving.

I believe there is a point to this and that is exception safety.
Suppose you have 2 + pointers that you new in the constructor
Suppose further that one of them might throw (or further down the line, another member object)

The constructor wiill gurantee that already constructed member objects will have the their destructors called before the throw
continues. But the bald pointers are not objects therefore there is a memory leak. delete or delete[] is not called.

In contrast, auto_ptr's will be correctly destroyed.
The lesson is if you think your sub-objects might throw
=> better use a RAII technique to wrap those bald pointers.
Any container is better than none.

This is about the only benefits of using auto_ptr here.

Stephen Howe

==============================================================================
TOPIC: Loop generates never-ending sockets and threads, need help debugging
http://groups.google.com/group/comp.lang.c++/t/bfb43e94d5fe70d1?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 3:16 pm
From: Jorgen Grahn

On Sat, 2010-02-06, Branimir Maksimovic wrote:
> Kurt wrote:
> While on the subject of threads and sockets,
>> do you have any books to recommend?
>
> Unix network programming, Richard Stevens.
> http://en.wikipedia.org/wiki/W._Richard_Stevens

Although that's for Unix, and the poster appeared to use some other
system. Stevens covers Unix and its variations, but not e.g. Windows.

For threads, I think you need more than Stevens -- I don't think he
teaches you to avoid all the pitfalls which makes all threaded code
I've seen a complicated, inefficient, and broken mess.

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

==============================================================================
TOPIC: Style guides for C and/or C++
http://groups.google.com/group/comp.lang.c++/t/3543d1f01ca9b305?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Feb 6 2010 3:26 pm
From: Jorgen Grahn

On Tue, 2010-01-19, Vicent Giner-Bosch wrote:
> I've been searching at this forum and at the Internet for style
> guides for C and/or C++, and I've found these ones:
>
> http://www.psgd.org/paul/docs/cstyle/cstyle.htm
> http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml
>
> Also, I've read some threads about C style matters. I think there is
> really a lot of stuff!
>
> I just would like to ask you for a quick answer to this question:
> which style guide or style rules do you recommend me to use when
> writing C/C++ code? It would be great if many of you would answer, so
> we all could have here a thread with a good summary about this
> subject.

You'll get no consensus or summary, that's for sure. Too many
different styles and opinions.

> PS: I've also posted this theme at comp.lang.c, so I apologize for
> cross-posting.

Thanks for mentioning it. Note that C and C++ are different
languages, and you cannot just mindlessly use the same style in both.

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

== 2 of 2 ==
Date: Sat, Feb 6 2010 3:42 pm
From: Jorgen Grahn

On Tue, 2010-01-19, Timothy Madden wrote:
> Vicent Giner-Bosch wrote:
> [...]
>> I just would like to ask you for a quick answer to this question:
>> which style guide or style rules do you recommend me to use when
>> writing C/C++ code? It would be great if many of you would answer, so
>> we all could have here a thread with a good summary about this
>> subject.
>
> I write C++ and I use the following indentation which I care about:
>
> template< typename charT, typename traits=char_traits<charT> >
> class charConvertor
> {
> public:
> static
> std::basic_string<charT> strMessage;
>
> template<typename ExternalCharType>
> static
> inline
> void Transcode(ExternalCharType const *szMessage)
> {
> strMessage = szMessage;
> }
> }
> convertor;
>
> int main()
> {
> int iResult = 0;
>
> if
> (
> iResult <= 10
> &&
> iResult >= -2
> &&
> iResult == 0
> )
> {
> cout << "Right result";
> cout << endl;
>
> return iResult;
> }
> else
> ::CreateWindow
> (
> szClassName,
> szTitle,
> dwStyle,
> xPos,
> yPos,
> cxWidth,
> cxHeight,
> hwndParent
> );
>
> return -1;
> }
>
>
> It looks better with syntax highlighting though ... :)
>
> My tab characters are 8 columns wide, although some editors made it a
> habit to use tab stops at 4 columns...
>
> I really do not understand the style some people use for blocks:
>
> int ProcessIndex(int iIndex) {
> return iIndex * 3 / 4;
> }
>
>
> It is so ugly and un-intuitive ...

Since you brought it up, I find *your* style extremely ugly and hard
to read. I've seen nothing like it before.

The style you say is ugly and used by "some people" is very common,
and used by people like Stroustrup. (Maybe not for function
definitions like in your example, but for most other blocks.) If you
have problems reading it, learn to. Otherwise you'll have problems
working with just about any other C++ programmer.

For reference, I would have written your code like this:

int main()
{
const int i = 0;

if(i<=10 && i>=-2 && i==0) {
std::cout << "Right result\n";
return 0;
}

::CreateWindow(name, title, style,
x, y,
width, height,
parent);

return 1;
}

(I don't believe in returning -1 from main().)

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

==============================================================================
TOPIC: PHP to C++: HipHop for PHP ...thoughts?
http://groups.google.com/group/comp.lang.c++/t/a14b64504ddfa510?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 3:56 pm
From: Brian

On Feb 6, 4:16 pm, Kensai <kens...@gmail.com> wrote:
> On 6/2/2010 8:54 μμ, Brian wrote:
>
> > Southwest Airlines dumped PERL for performance reasons ten
> > years ago and started using C++. I'm not real impressed
> > that Facebook has learned the lesson though. They seem
> > to be coming to C++ kicking and screaming.
>
> C++ is greener as well. Well not according to everyone, but performance
> is always a consideration once your service becomes important.
>

It should be a consideration before a service becomes
popular. If you fail to plan (for success), I think
you plan to fail.

I suggest being ruthless when it comes to scripts
and programs in other languages that someone wants
to write. They look helpful and harmless, but they
turn into monsters overnight if you aren't careful.
You can pay now or pay more later. Facebook like
many others, said in reply, "No thanks." Now
though, they're biting the bullet for their past
ways.

Brian Wood
http://webEbenezer.net

"Where there is no vision, the people perish: but he
that keeps the law, happy is he." Proverbs 29:18

==============================================================================
TOPIC: Why does a vector fail here?
http://groups.google.com/group/comp.lang.c++/t/0f7f65bf6f4a8aa4?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 3:57 pm
From: Jorgen Grahn

On Sun, 2010-01-24, JoeC wrote:
> I am writing a program to display bitmaps and I want to use a vector
> to hold my bitmap data but when I use this algorithm it fails:
>
> for(index = 0; index < dwn; index++){
> memcpy(&temp[((dwn-1) - index)*acc],
> &bitData[index*acc],acc);}

This is completely out of context so I have no idea what you're doing,
but memcpy() is dangerous (and almost always pointless) to use on
anything which may be an object -- for example a std::vector.

(It's also used pointlessly surprisingly often in C code -- I have
lost count of all the complicated memcpy() calls I've replaced
with straight struct assignments over the years.)

...
> Anything else I can add
> to help explain the problem. I often have problems asking questions
> on more complex problems because it can be cumbersome to post from
> several files both .h and .cpp.

http://en.wikipedia.org/wiki/Pastebin

perhaps with the core part of the problem quoted in the posting.

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

==============================================================================
TOPIC: Motivation of software professionals
http://groups.google.com/group/comp.lang.c++/t/21a3fdec4dd53e6a?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 3:57 pm
From: "Hillbilly"

Which is why I rarely participate as they are ALWAYS FUBAR and BIASED.

"Richard Cornford" <Richard@litotes.demon.co.uk> wrote in message
news:62cdf238-b5ce-4d42-aaa0-1ebe099a01d9@k41g2000yqm.googlegroups.com...
> On Feb 5, 11:19 am, Stefan Kiryazov wrote:
>> Hi all,
>>
>> I am doing a research about motivation in software development,
>> the most efficient practices to motivate software engineers,
>> their popularity, etc.
>
> Strange question; the most efficient motivator of professionals is
> money, and money is very popular.
>
>> As a part of the research, I am doing an online survey for
>> software engineers and managers in software development.
> <snip>
>
> This would be more convincing as an academic exercise, as opposed to,
> say, spam intended to encourage visitors to some web page with the
> intention of gaining advertising revenue, if there were not so many
> advertisements on the page.
>
> In any event, your survey needs the addition of a large number of
> "This question makes no sense" option checkboxes, as it is
> unanswerable as it is.
>
> Richard.

==============================================================================
TOPIC: How to identify the exe file associated with core dump
http://groups.google.com/group/comp.lang.c++/t/ae385d53872a2543?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 4:11 pm
From: Jorgen Grahn

On Mon, 2010-01-25, Vladimir Jovic wrote:
> mthread wrote:
>> Hi,
>> We have multiple applications(C & C++) running in our system. When
>> a core dump is generated we did not know which application caused the
>> core dump. Is there a way to find the application name from the core
>> dump file. Kindly help me on this issue.
>
> See this:
> http://www.sinz.org/Michael.Sinz/Linux/core.html
[Linux kernel patch which lets you control the core dump file name]

Interesting, but in a way not helpful: since the core dump already
contains the process name, making the file name contain it too adds no
information.

Even more offtopic: I find naming core files counter-productive in
practice. If your software is broken and tends to crash, named core
dumps will eventually make someone decide to *disable* core dumps, to
avoid filling the disk. And then you are stuck with no information at
all for your C++ debugging sessions.

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

==============================================================================
TOPIC: A design question ....
http://groups.google.com/group/comp.lang.c++/t/50b88a38cf4c0097?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Feb 6 2010 4:42 pm
From: forums_mp@hotmail.com

#include <iostream>
#include <typeinfo>
#include <vector>

/// BEGIN "UNTOUCHABLE" CLASSES AND DATA
INSTANTIATORS ///////////////
class base {
public :
//handful of stuff
virtual ~base() {}
};

/*
one of many untouchable pn derived classes with
methods not found in base class
*/
class p1 : public base {
int value ;
public :
p1()
: value ( 0 )
{}
void set_something ( int in ) { value = in ; }
int get_something() const { return ( value ) ; }
~p1() {}
};

class p2 : public base {
public :
//stuff
~p2() {}
};
//up to pn
/// END "UNTOUCHABLE" Pn CLASSES AND DATA
INSTANTIATORS /////////////////

/*
============================================================
holder is a collection of UNTOUCHABLE classes, with useful
member data (For example) 'count'. For each call to Set_ a
phandler will
increment count
*/
typedef unsigned int unsigned_type ;
struct holder {
unsigned_type holder_id ;
unsigned_type count ;
static base *ptr ;
holder ( base *ptr_, unsigned_type const id )
: holder_id ( id )
{
ptr = ptr_;
}
virtual ~holder() { }
};
base* holder::ptr = 0 ;
typedef std::vector < holder* > holder_vec ;

/*
============================================================
base handler for d's.
notified upon receipt of a client message
*/
class d_handler_base {
public :
virtual void process() = 0 ;
virtual ~d_handler_base() {}
};
class d1_handler : public d_handler_base
{
holder_vec hv ;
//only interested in p1 objects located in the holder containers
p1* ptr_p1 ;

public :
d1_handler ( holder_vec& in )
: hv ( in )
//NOTE!!!!!!!!!!!!!!!!!
//ideally i need to use a map so i could interate and FIND p1
//for now we'll assume p1 exists at location 0 within holder_vec
, ptr_p1 ( static_cast < p1* > ( hv [ 0 ]->ptr ) )
{}
void process ()
{
unsigned_type const dummy = ptr_p1->get_something() ;
std::cout << std::hex << "0x" << dummy << std::endl;
}
};
class d2_handler : public d_handler_base
{
public :
d2_handler ()
{}
void process ()
{
std::cout <<"." << std::endl;
}
};

/*
============================================================
base handler for p's.
notified upon receipt of a server message
*/
class p_handler_base {
public :
virtual ~p_handler_base() {}
};
class p1_handler : public p_handler_base
{
holder_vec& hv;
p1* ptr_p1 ;

public :
p1_handler ( holder_vec& in )
: hv ( in )
, ptr_p1 ( static_cast < p1* > ( hv [ 0 ]->ptr ) )
{}
void update_p_msg ( unsigned_type const in ) {
ptr_p1->set_something ( in ) ;
hv [ 0 ]->count ++ ;
}
};

int main() {
static holder_vec hv ;
//this 'new new' stuff seems unsightly... i think a map would be
better....
// for now create a p1 with its id of 0x400, similarily a p2 with
it's id 0x500
hv.push_back ( new holder ( new p1(), 0x400 ) ) ;
hv.push_back ( new holder ( new p2(), 0x500 ) ) ;

d1_handler *ptrd1 = new d1_handler ( hv ) ;
p1_handler *ptrp1 = new p1_handler ( hv ) ;
//change
ptrp1->update_p_msg( 0xCAFE ) ;
ptrd1->process() ;

//change
ptrp1->update_p_msg( 0xDEAD ) ;
ptrd1->process() ;

std::cin.get() ;

}

In a nutshell:

Common message holder class (named holder) with a collection of base
classes. Within main a p1_handler object initiates a change to a p1
object (via the call to set_something). The d1_handler observes the
change.

At this juncture you may say this 'screams' an event handler (perhaps
observer implementation). This way any change to a Pn message by a Pn
handler is dispatched to a Dn handler.

My answer to an event handler (observer implementation) is No!
Here's why: Referencing the d1 and d2 handler classes within source
above:

a) Not all Dn handlers is interested in Pn (UNTOUCHABLE) messages.
For instance, the message holder vec holding Pn messages is a
_dont_care_ for a d2_handler.

b) For those Dn handler interested in Pn messages (i.e d1_handler),
these Dn handlers are not interested in being notified of immediate
changes to Pn messages by Pn handlers. These Dn handlers is only
interested in knowing they have the 'latest' Pn message _whenever_
(600 updates could have occurred since) they access a Pn message
object.

From a development perspective, here's where I'm struggling with in
this case C++. The design and what (perhaps) pattern to use to
achieve the objective. After scanning the GOF here are my thoughts:

1) Leave well enough alone. Current implementation works but then I'm
often not satisfied given my struggles
2) Add a proxy class between the Pn handlers and Dn handlers. I
suspect this would be beneficial to the Dn handlers (more so that Pn
handler since a Pn message could be local to a Pn handler). In doing
so the Dn handler could request via the Proxy for a Pn message and
receive the 'lastest/most up to date' Pn message. The drawback here is
the overhead and (worse) I'm not sure how to implement a proxy (at
least not yet)
3) Perhaps a common base class between Pn handlers and Dn handlers
would suffice.

My question is - is there a better way to do this? Thoughts/ideas
welcomed.

Thanks in advance

== 2 of 2 ==
Date: Sat, Feb 6 2010 4:59 pm
From: "ng2010"

Whoa! That's a lot of code and verbage to be a "design" question! Is
there really no higher-level way to express your "design" issue?

forums_mp@hotmail.com wrote:
> #include <iostream>
> #include <typeinfo>
> #include <vector>
>
> /// BEGIN "UNTOUCHABLE" CLASSES AND DATA
> INSTANTIATORS ///////////////
> class base {
> public :
> //handful of stuff
> virtual ~base() {}
> };
>
> /*
> one of many untouchable pn derived classes with
> methods not found in base class
> */
> class p1 : public base {
> int value ;
> public :
> p1()
> : value ( 0 )
> {}
> void set_something ( int in ) { value = in ; }
> int get_something() const { return ( value ) ; }
> ~p1() {}
> };
>
> class p2 : public base {
> public :
> //stuff
> ~p2() {}
> };
> //up to pn
> /// END "UNTOUCHABLE" Pn CLASSES AND DATA
> INSTANTIATORS /////////////////
>
>
> /*
> ============================================================
> holder is a collection of UNTOUCHABLE classes, with useful
> member data (For example) 'count'. For each call to Set_ a
> phandler will
> increment count
> */
> typedef unsigned int unsigned_type ;
> struct holder {
> unsigned_type holder_id ;
> unsigned_type count ;
> static base *ptr ;
> holder ( base *ptr_, unsigned_type const id )
> : holder_id ( id )
> {
> ptr = ptr_;
> }
> virtual ~holder() { }
> };
> base* holder::ptr = 0 ;
> typedef std::vector < holder* > holder_vec ;
>
> /*
> ============================================================
> base handler for d's.
> notified upon receipt of a client message
> */
> class d_handler_base {
> public :
> virtual void process() = 0 ;
> virtual ~d_handler_base() {}
> };
> class d1_handler : public d_handler_base
> {
> holder_vec hv ;
> //only interested in p1 objects located in the holder containers
> p1* ptr_p1 ;
>
> public :
> d1_handler ( holder_vec& in )
> : hv ( in )
> //NOTE!!!!!!!!!!!!!!!!!
> //ideally i need to use a map so i could interate and FIND p1
> //for now we'll assume p1 exists at location 0 within holder_vec
> , ptr_p1 ( static_cast < p1* > ( hv [ 0 ]->ptr ) )
> {}
> void process ()
> {
> unsigned_type const dummy = ptr_p1->get_something() ;
> std::cout << std::hex << "0x" << dummy << std::endl;
> }
> };
> class d2_handler : public d_handler_base
> {
> public :
> d2_handler ()
> {}
> void process ()
> {
> std::cout <<"." << std::endl;
> }
> };
>
> /*
> ============================================================
> base handler for p's.
> notified upon receipt of a server message
> */
> class p_handler_base {
> public :
> virtual ~p_handler_base() {}
> };
> class p1_handler : public p_handler_base
> {
> holder_vec& hv;
> p1* ptr_p1 ;
>
> public :
> p1_handler ( holder_vec& in )
> : hv ( in )
> , ptr_p1 ( static_cast < p1* > ( hv [ 0 ]->ptr ) )
> {}
> void update_p_msg ( unsigned_type const in ) {
> ptr_p1->set_something ( in ) ;
> hv [ 0 ]->count ++ ;
> }
> };
>
>
> int main() {
> static holder_vec hv ;
> //this 'new new' stuff seems unsightly... i think a map would be
> better....
> // for now create a p1 with its id of 0x400, similarily a p2 with
> it's id 0x500
> hv.push_back ( new holder ( new p1(), 0x400 ) ) ;
> hv.push_back ( new holder ( new p2(), 0x500 ) ) ;
>
> d1_handler *ptrd1 = new d1_handler ( hv ) ;
> p1_handler *ptrp1 = new p1_handler ( hv ) ;
> //change
> ptrp1->update_p_msg( 0xCAFE ) ;
> ptrd1->process() ;
>
> //change
> ptrp1->update_p_msg( 0xDEAD ) ;
> ptrd1->process() ;
>
>
> std::cin.get() ;
>
> }
>
> In a nutshell:
>
> Common message holder class (named holder) with a collection of base
> classes. Within main a p1_handler object initiates a change to a p1
> object (via the call to set_something). The d1_handler observes the
> change.
>
> At this juncture you may say this 'screams' an event handler (perhaps
> observer implementation). This way any change to a Pn message by a Pn
> handler is dispatched to a Dn handler.
>
> My answer to an event handler (observer implementation) is No!
> Here's why: Referencing the d1 and d2 handler classes within source
> above:
>
> a) Not all Dn handlers is interested in Pn (UNTOUCHABLE) messages.
> For instance, the message holder vec holding Pn messages is a
> _dont_care_ for a d2_handler.
>
> b) For those Dn handler interested in Pn messages (i.e d1_handler),
> these Dn handlers are not interested in being notified of immediate
> changes to Pn messages by Pn handlers. These Dn handlers is only
> interested in knowing they have the 'latest' Pn message _whenever_
> (600 updates could have occurred since) they access a Pn message
> object.
>
> From a development perspective, here's where I'm struggling with in
> this case C++. The design and what (perhaps) pattern to use to
> achieve the objective. After scanning the GOF here are my thoughts:
>
> 1) Leave well enough alone. Current implementation works but then I'm
> often not satisfied given my struggles
> 2) Add a proxy class between the Pn handlers and Dn handlers. I
> suspect this would be beneficial to the Dn handlers (more so that Pn
> handler since a Pn message could be local to a Pn handler). In doing
> so the Dn handler could request via the Proxy for a Pn message and
> receive the 'lastest/most up to date' Pn message. The drawback here is
> the overhead and (worse) I'm not sure how to implement a proxy (at
> least not yet)
> 3) Perhaps a common base class between Pn handlers and Dn handlers
> would suffice.
>
> My question is - is there a better way to do this? Thoughts/ideas
> welcomed.
>
> Thanks in advance

==============================================================================
TOPIC: PODs, Constructors and the Boost uuid Class
http://groups.google.com/group/comp.lang.c++/t/a115833b71eecd59?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Feb 6 2010 5:03 pm
From: "ng2010"

From http://www.boost.org/doc/libs/1_42_0/libs/uuid/uuid.html and in the
section titled "POD Efficiencies", they give a workaround to the
defficiency/oversight in C++ that a POD cannot have constructors:

class uuid_class : public boost::uuids::uuid
{
public:
uuid_class() // def ctor shouldn't auto gen IMO else this
// class should be called auto_uuid or something
: boost::uuids::uuid(boost::uuids::random_generator()())
{}

explicit uuid_class(boost::uuids::uuid const& u)
: boost::uuids::uuid(u)
{}

operator boost::uuids::uuid() {
return static_cast<boost::uuids::uuid&>(*this);
}

operator boost::uuids::uuid() const {
return static_cast<boost::uuids::uuid const&>(*this);
}
};

What I don't understand is why the conversion operators in uuid_class
above guarantee anything more than just having defined boost::uuids::uuid
as a class with the constructors given above. The conversion operators
for the operators are just casting *this. Why the operators at all when
uuid_class IS a uuid?

== 2 of 2 ==
Date: Sat, Feb 6 2010 10:10 pm
From: "Alf P. Steinbach"

* ng2010:
> From http://www.boost.org/doc/libs/1_42_0/libs/uuid/uuid.html and in the
> section titled "POD Efficiencies", they give a workaround to the
> defficiency/oversight in C++ that a POD cannot have constructors:
>
> class uuid_class : public boost::uuids::uuid
> {
> public:
> uuid_class() // def ctor shouldn't auto gen IMO else this
> // class should be called auto_uuid or something

No, that would be unsound design. There is already the POD class if you want an
uninitialized UUID instance. This class would serve no purpose if did nothing. :-)

> : boost::uuids::uuid(boost::uuids::random_generator()())
> {}
>
> explicit uuid_class(boost::uuids::uuid const& u)
> : boost::uuids::uuid(u)
> {}
>
> operator boost::uuids::uuid() {
> return static_cast<boost::uuids::uuid&>(*this);
> }
>
> operator boost::uuids::uuid() const {
> return static_cast<boost::uuids::uuid const&>(*this);
> }
> };
>
> What I don't understand is why the conversion operators in uuid_class
> above guarantee anything more than just having defined boost::uuids::uuid
> as a class with the constructors given above. The conversion operators
> for the operators are just casting *this. Why the operators at all when
> uuid_class IS a uuid?

It appears to be meaningless.

With Boost stuff one can never say for sure because those guys are very very
heavily into SFINAE and other subtle template metaprogramming magic and other
at-the-very-front-edge things (I think that's a problem with Boost), but at
least for ordinary programming it's meaningless to have the operators above.

But notwithstanding my comment about Boost intricacies I'm fairly sure that it's
an error, perhaps something left from an earlier version with private
inheritance, because this class lacks an assignment operator that directly takes
a POD argument, and although it will work without it (via value conversion)
that's inefficient so if this example had been quality checked then that
assignment operator would have been there, so, it's not been checked.

Cheers & hth.,

- Alf

==============================================================================
TOPIC: Static const variables cause linker problems under Qt
http://groups.google.com/group/comp.lang.c++/t/f7acbdcaf443120e?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 5:13 pm
From: Yu Han

On 02/05/2010 11:24 PM, Rune Allnor wrote:
> Hi all.
>
> I have a template class where I have defined some
> constants in a header file, along the lines of
>
> ////////////////////////////////////////////
> class flags{
> static const size_t flag;
> };
>
> const size_t flags::flag = 1;
> ////////////////////////////////////////////
try this:
class flags {
static const size_t flag = 1;
};
>
> This compiles and runs nicely in the Boost.Test program,
> but when I try to use the template class in a Qt GUI program,
> the linker starts complaining about the constants as being
> multiple defined objects:
>
> - in main.obj
> - in moc_myfile.obj
> - in myfile.obj
>
> I have included the standard guard about multiple inclucions
> of the header files, and I can see why these constants would
> appear in myfile.obj, as I include the file where they are declared
> from myfile.h. However, I have no idea why the constants should
> be available in main.obj or moc-myfile.obj - that's where Qt come
> in to do its thing.
>
> There isn't much I can do about the ways Qt twists and turns
> the code into an executable, so I suppose my only hope
> is to be able to resolve the 'multiple definition' problem.
>
> Any hints on how to do this?
>
> The flags class will exist in millions of instances, so I can not
> afford to include the flag definintions as const variables in the
> class.
>
> Rune

--
Yu Han

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

==============================================================================
TOPIC: ===Welcome to comp.lang.c++! Read this first.
http://groups.google.com/group/comp.lang.c++/t/a801c2fa8f66c0a0?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Feb 6 2010 9:30 pm
From: Shiva

Welcome to comp.lang.c++! Read this first.

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-----------------
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Borland C++ Builder
-------------------
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borland.public.cpp.language
borland.public.cppbuilder

-Shiva
http://www.slack.net/~shiva/welcome.txt

Sun Feb 7 00:30:00 EST 2010

==============================================================================
TOPIC: paypal wholesale Puma (paypal payment)(www.globlepurchase.com)
http://groups.google.com/group/comp.lang.c++/t/47a934a1b114096e?hl=en
==============================================================================

== 1 of 1 ==
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