> In article <WOOGm.1013$Js....@newsfe10.iad>, spambus...@prodigy.net > says... > [ ... ] > > > If you look at it closely, you'll see that the standard > > > doesn't actually give any guarantees with regards to > > > standard layout and other languages, for the reason stated > > > above. > > 'Care to restate that reason? > The bottom line is pretty simple: something like 'extern "C"' > is really trying to give a guarantee about a C compiler, but > the C++ standard doesn't really have any control over C > compilers. You can only accomplish something useful with > 'extern "C"' by having a C compiler that's written to > cooperate with your C++ compiler -- but the C++ standard can't > really do anything about that, and for that matter the C > standard really can't either.
It's not quite that bad; you don't need active cooperation with the C compiler. You do need a C compiler, however, and you need to know what it does and generates in order to make ``extern "C"'' work in C++.
> > > There may be some advanced programming techniques which > > > depend on standard layout, but for the everyday user, the > > > only really significant distinction is whether the class > > > could be written in C or not > > You meant if a class could look like a struct to C, surely. > I think what he's saying (in effect) is that the main time > PODs matter or get used, is when you have a header that you > can compile as either C or C++, and you want to have (at least > some) assurance of compatibility between the two.
Exactly. Otherwise, you're not generally too concerned with POD-ness in itself, only certain properties of it (allows agglomerate initialization---but a lot of non-PODs do that---or static initialization).
One interesting idea that I've never seen done would be to conditionally add convenience functions in the header, something like:
> [ ... ] > In C++ 0x, however, there's an "=default" syntax that allows > you to tell the compiler to generate a default ctor, copy > ctor, copy assignment operator, and/or dtor, even if you > _have_ defined some other ctor. For example: > class X { > int data; > public: > X(int val) : data(val) {} > X() = default; > X(x const &) = default; > X &operator=(X const &other) = default; > ~X() = default; > }; > Now, we have a user-defined ctor that takes a value of type > int that is used to initialize the data member -- but we also > have explicitly defaulted the definitions of the other special > member functions, so they remain "trivial" and the type is > still a POD.
Just curious, but what effect does this have on static initialization using the agglomerate syntax. Can I still write something like:
static X const table[] = { 1, 2, 3 };
and be guaranteed that the initialization precedes all code that I've written (including code in constructors of static objects)?
On Oct 31, 4:19 am, "dragan" <spambus...@prodigy.net> wrote:
> James Kanze wrote: [...] > >> I downloaded N2960. I like to think in terms of the things > >> a POD can or cannot have rather than the lingo like: > >> trivially copyable, trivial class, standard layout, and on > >> and on. In another post I wrote my understanding of what is > >> and isn't allowed. > > The problem is that you can't express the requirements in > > terms of can or cannot have. > Why is that? Is it so absolutely, or just because we are > talking about C++?
It's because the actual requirements contain several "must have", not can have or cannot have.
> > At least partially, you have to express them in terms of > > "must have": a POD must have a trivial default constructor, > > for example (which is not the same thing as not having a > > non-trivial default constructor---you have three > > possibilities: no default constructor, trivial default > > constructor and non-trivial default constructor). > But by "requirements", you mean "required by an > implementation", yes?
No. I mean the requirements on a class for it to be a POD.
On Oct 31, 4:25 am, "dragan" <spambus...@prodigy.net> wrote:
> James Kanze wrote: > > On Oct 29, 4:23 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote: > >> In article <VV%Fm.41268$EU5.38...@newsfe05.iad>, > >> spambus...@prodigy.net says...
[...]
> > Attention: the requirement isn't that the class not have a > > non-trivial X; it is that it have a trivial X. Thus, for > > example: > > struct S { S( int ); int i; }; > > doesn't have a non-trivial default constructor, but it > > doesn't have a trivial one either, and thus, is not a POD. > Is it still layout-compatible with C though?
In practice, with most compilers, yes.
The current standard doesn't talk about "layout-compatible", and no C++ standard can impose anything on the C compiler. I didn't see anything in N2914 (the latest draft that I happen to have handy) that guaranteed that a "standard-layout" class is in anyway compatible with C.
On the other hand, the whole concept of "layout-compatible" seems to have been lifted from the C standard, and from a QoI point of view, I would expect that anything with "standard-layout" be compatible with C if the system defines a standard C ABI (as most do).
> (I'm not sure of the usefullness of "POD" anymore).
Per se, they don't have much use. They do restrict the implementation in some ways, however, that typically allows them to be used in mixed language headers (headers which are used by both C and C++).
> > IIUC, in the next version of the standard, you will be able > > to write: > > struct S { S( int ); S() = default; int i; }; > > and it will have the required trivial default constructor. > And what will the compiler do with such a trivial default > constructor?
Nothing. Otherwise, the constructor wouldn't be trivial.
> Why does it need to enslave that thing?
I'm not sure what you're trying to ask there, but if it is "why do we need a special syntax for this?", it's because the current standard says that if a class has any constructor, the compiler won't provide a default constructor implicitly, and a lot of code counts on this.
In article <1c83cc8c-9e7a-457a-bf85- cfd3c93ad...@b15g2000yqd.googlegroups.com>, james.ka...@gmail.com says...
[ ... ]
> It's not quite that bad; you don't need active cooperation with > the C compiler. You do need a C compiler, however, and you need > to know what it does and generates in order to make ``extern > "C"'' work in C++.
I was thinking primarily of the fact that anytime the C compiler changes anything about its ABI, the C++ compiler needs to know about it and take steps to compensate. Fortunately, at least in most cases the ABI is fairly stable, so this doesn't arise a lot in practice.
[ ... ]
> One interesting idea that I've never seen done would be to > conditionally add convenience functions in the header, something > like:
> In practice, I'm sure that this will work, but formally...
In practice, it's likely to work at least as long as none of the functions is virtual. A virtual function would stand a good chance of causing breakage though...
[ ... ]
> Just curious, but what effect does this have on static > initialization using the agglomerate syntax. Can I still write > something like:
> static X const table[] = { 1, 2, 3 };
> and be guaranteed that the initialization precedes all code that > I've written (including code in constructors of static objects)?
I haven't studied that in a lot of detail yet, but it looks like there's a fair bit of new material to study. First of all, they've added thread local storage, and associated initialization rules for it. Then they've added constexpr's, which allow static initialization in quite a few cases that it wouldn't work in C++ 98/03.
Those have caused enough changes to the text that I haven't yet sorted out whether the underlying rules have changed a lot, or whether it's mostly just different text describing mostly similar rules with a couple of new possibilities thrown into the mix.
> On Oct 31, 4:12 am, "dragan" <spambus...@prodigy.net> wrote:
> > James Kanze wrote: > > > On Oct 29, 11:40 pm, "dragan" <spambus...@prodigy.net> wrote: > > I think "aggregate" gets thrown around so much, but it should > > probably be reserved more for implementer-level discussion > > rather than user-level. It seems so minor relative to the > > notion of POD (or layout compatibility! Errgh, so > > frustrating!).
> Yes and no. For the user, aggregate initialization can be an > advantage in certain cases, e.g. my examples of letting the > compiler calculate array size. For the user, there are really > three things which interesting:
> 1. Aggregate initialization: useful for letting the compiler > calculate the size of an array, and in general for static > data.
> 2. Static initialization, for avoiding order of initialization > issues. This requires trivial constructors and constant > expressions in the initializer; for compound types (struct's > and arrays), the type must be an aggregate, and aggregate > initialization must be used. (Otherwise, you must have a > constructor somewhere, and the type ceases to be trivial.)
> 3. PODs or layout compatibility: mainly important with regards > to communicating with other languages, especially C. (The > system API is generally defined in terms of C these days.)
> > >> I think POD may be the key thing for layout compatibility > > >> with C and probably other languages. PODs no longer have to > > >> be aggregates in C++0x: they can have constructors, just > > >> not default or copy constructors, and no copy assignment > > >> operator. (N2690). > > > Layout compatibility is an awkward problem. C++ can mandate > > > a certain number of things with regards to how the C++ > > > compiler lays out data, but it can't mandate anything with > > > regards to how other languages layout data. In the end, > > > it's a lot like the ``extern "C"'' fiasco: C++ requires a > > > compiler to support it, stating that functions declared > > > ``extern "C"'' must be callable from C (or something along > > > those lines). Which is all nice and fine, but what does it > > > mean if the platform doesn't have a C compiler? Or if it > > > has several C compilers, with different calling conventions? > > "extern C" fiasco? News to me that it was a fiasco (you must > > be an implementor/insider, I bet)! I thought it was more like > > "thank god we can still use DLLs in C++".
> Fiasco may be too strong a word, but formally, the standard > guarantees much less than it seems to. (I certainly doesn't > guarantee anything with regards to DLLs, for example.) All that > it says (with regards to C) is ``Every implementation shall > provide for linkage to functions written in the C programming > language, "C", and linkage to C + + functions, "C++".'' Except > that it doesn't specify how these "functions written in the C > programming language" are to be compiled or linked; an > implementation may require you to compile them using a special C > compiler, which generates code incompatible with the system API, > for example. And it doesn't address the issue of what to do if > there is no C compiler for the system.
> At least some of the people involved with the standardization > proceedure are aware of this weakness, although the committee > doesn't seem to have wanted to address it. I think the general > intent is more along the lines that IF there is at least one C > implementation available on the platform, then the compiler must > support linkage with one of them, and document which one, and > what is necessary to make it work.
> The probable reason the committee didn't address the problem is > that it isn't one in practice. Practically all platforms that > support C++ have a standard C ABI, which is adhered to by all C > compilers, and practically all C++ compilers come with a C > compiler, and require no special steps to link C and C++. So > the standard may not say exactly what was wanted, but in > practice, everything works as was desired.
> Until the day someone decides that C is dead enough that they > don't need a C compiler for their platform.
> [...]
> > > If you look at it closely, you'll see that the standard > > > doesn't actually give any guarantees with regards to > > > standard layout and other languages, for the reason stated > > > above. > > 'Care to restate that reason?
> The C++ standard can't impose anything on other languages, only > on C++.
> > > There may be some advanced programming techniques which > > > depend on standard layout, but for the everyday user, the > > > only really significant distinction is whether the class > > > could be written in C or not > > You meant if a class could look like a struct to C, surely.
> More or less, yes. With the addition of non-virtual member > functions, but that's about it.
> > > ---if it could, it will be accessible from C, and probably > > > from most other languages as well (on typical small and > > > medium general purpose computers > > That covers a lot (the most of it?) of ground, and propably > > shouldn't be flattened.
> Typical small and medium general purpose computers represent but > a small percentage of all computers. I'd guess off hand that > something like 90% of all computers are embedded systems. At > the other end, and this is the place where I suspect most of the > problems come, are the mainframes. IBM System z doesn't define > everything in terms of C, at least under the traditional OS's. > (You can also get it with Linux.) Cobol is still the > predominant language there.
> > > ---I wouldn't count on it on mainframes, nor for that matter > > > on embedded systems); otherwise, it won't be. (You may, of > > > course, add non-virtual member functions, including > > > conversion operators, but not constructors, destructors or > > > assignment operators, without causing problems.) > > I'm still hoping that Mr. Coffin was right about "convenience > > constructors" being OK. (Else I'll have to research and find > > out why there cannot be such. I'll blindly accept the > > concrete "special functions" as being special and reserved, > > but I really would want to know why "convenience constructors" > > are a no-go, if indeed so).
> You can't add "convenience constructors" today, and I'm sure > that Jerry didn't say that. The next version of the standard > will allow it, I think, but only if you explicitly say you want > the "trivial" default constructor. And while initialization > syntax has been somewhat unified, I still don't think you can > get all of the features of aggregate initialization (especially > static initialization) if you provide any constructor; at most, > you'll be guaranteed a C compatible layout (but that's typically > the case today, with most compilers).
> > > The other thing that is often important is whether the class > > > is an aggregate which supports static initialization. But > > > in practice, the two overlap; there are very few cases where > > > you can use static aggregate initialization but couldn't > > > write the class in C. (The presence of a pointer to member > > > in the class would be an example of one.) > > I should have stopped responding to your post probably after I > > asked whether you meant the current standard or the yet-to-be > > (draft) C++. All of a sudden, I feel like I know NOTHING! > > Errrgh!! I think my house may explode if I start up Visual C++ > > and _I_ use it! I saw no red sticker on the box.. I got it for > > free as a download! ;)
> Unless I explicitly state otherwise, I'm talking about the > current standard. There are no implementations of the next > standard (can't be, since it doesn't exist yet), and the way > things are going, I'm beginning to wonder if there will be any > in my lifetime.
Perhaps what's needed are on line compilers that output fully instantiated code which can be handled by "existing" C++ compilers. By that I mean that some changes to existing compilers would be needed, but the changes would be relatively minor. That might help in terms of getting the new version of the language out and in use. Without doing something radically different, I think the number of C++0x compilers is likely to be less than the number of C++ compilers today. I hope you live to see C++0x in general use, but at the very least, I think things will be interesting (curioser and curioser) from here on in.
Jerry Coffin wrote: > In article <WOOGm.1013$Js....@newsfe10.iad>, spambus...@prodigy.net > says...
> [ ... ]
>>> If you >>> look at it closely, you'll see that the standard doesn't >>> actually give any guarantees with regards to standard layout and >>> other languages, for the reason stated above.
>> 'Care to restate that reason?
> The bottom line is pretty simple: something like 'extern "C"' is > really trying to give a guarantee about a C compiler, but the C++ > standard doesn't really have any control over C compilers. You can > only accomplish something useful with 'extern "C"' by having a C > compiler that's written to cooperate with your C++ compiler -- but > the C++ standard can't really do anything about that, and for that > matter the C standard really can't either.
Whatever happened with projects to bring forth a standard C++ ABI. Itanium only?
>>> There may be some >>> advanced programming techniques which depend on standard layout, >>> but for the everyday user, the only really significant >>> distinction is whether the class could be written in C or >>> not
>> You meant if a class could look like a struct to C, surely.
> I think what he's saying (in effect) is that the main time PODs > matter or get used, is when you have a header that you can compile as > either C or C++, and you want to have (at least some) assurance of > compatibility between the two.
I would think that cross-platform interoperability is a larger concern. At least with a C ("POD") struct, you stand a chance at it looking the same in more than one machine. Not hardly so for classes (I mean with one using all the C++ "fancy" things).
> [ ... ]
>> I'm still hoping that Mr. Coffin was right about "convenience >> constructors" being OK. (Else I'll have to research and find out >> why there cannot be such. I'll blindly accept the concrete "special >> functions" as being special and reserved, but I really would want >> to know why "convenience constructors" are a no-go, if indeed so).
> Yes -- to be a POD, the default ctor, copy ctor and dtor must all be > trivial. A trivial ctor must be generated by the compiler -- any user > defined ctor is non-trivial. Even if it's carefully written to do > exactly what a compiler-generated ctor would have done, the fact that > you wrote it still means it's non-trivial.
I understand all that and am accepting of it.
> In C++ 98/03, if you define any ctor, that prevents the compiler from > generating a default ctor. > If you want a default ctor, you need to > define one, and by definition, when/if you do so, it won't be a > trivial ctor. Likewise with the dtor, copy ctor and copy assignment > operator.
I've probably encountered that, but I didn't "know" that. So are you retracting your statement that "convenience constructors" are allowed?
> In C++ 0x, however, there's an "=default" syntax that allows you to > tell the compiler to generate a default ctor, copy ctor, copy > assignment operator, and/or dtor, even if you _have_ defined some > other ctor. For example:
> class X { > int data; > public: > X(int val) : data(val) {} > X() = default; > X(x const &) = default; > X &operator=(X const &other) = default; > ~X() = default; > };
OK, things are looking rosie then for C++0x. A good enough reason to drop the current lineup ASAP, IMO. Hopefully the C++0x goodies will start trickling into compilers even before "ratification" or whatever they call it.
> Now, we have a user-defined ctor that takes a value of type int that > is used to initialize the data member -- but we also have explicitly > defaulted the definitions of the other special member functions, so > they remain "trivial" and the type is still a POD.
And that makes me a happy camper, cuz not allowing "convenience constructors" is a pet peave of mine. I saw/see no reason why it has to be without them, so now I know indeed there was no reason other than oversight.
> One other strange wrinkle: it's possible to create a non-trivial > special member function using the '= default;' syntax. To be trivial, > the function must (among other things) be inline, and the > '=default;' must be on the _declaration_ of the function. If (for > whatever strange reason) you choose to, you can do something like:
> class Y { > // ... > public: > Y(); > };
> Y::Y() = default;
> You've now explicitly defaulted the default ctor, BUT the '=default' > isn't on the initial declaration, and your definition is _not_ an > inline function, so it's no longer trivial.
I would have assumed that the out-of-line Y::Y() would not allow "=default"! The question becomes: Why does it?! Hehe, so Scott Meyers can right more "Effective C++" books! (Great series by the way, but if it ever becomes contrived... oh nevermind).
>> (Aside: Are overloaded operators fast compared to functions? I >> don't know why that sticks in my mind. Yeah I know, I could test >> it, but I think in the past I have and have found that. I may be >> mistaken).
> An overloaded operator _is_ a function -- it just has a rather > different name than most other functions. Overloaded operators are > typically quite short functions, so there's a good chance that the > compiler can generate inline code. Nonetheless, the fact that it's an > overloaded operator does not (in itself, at least with any compiler > I've ever seen or heard of) make any difference in whether the code > will be generated inline. The code generation depends on the size and > complexity of the function, not the name it's given.
Alright. Maybe long ago when that stuck in my mind I had experienced the inline vs. online thing. But I get most of my information from books (and lately online) and "operators are FAAAST!" sticks in my mind, so I think I may have read it somewhere. It makes perfect sense to me that operators are no different than functions except for the obvious syntax. Oh well, could have been a brainfart.
James Kanze wrote: > On Oct 31, 4:12 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: >>> On Oct 29, 11:40 pm, "dragan" <spambus...@prodigy.net> wrote:
>> I think "aggregate" gets thrown around so much, but it should >> probably be reserved more for implementer-level discussion >> rather than user-level. It seems so minor relative to the >> notion of POD (or layout compatibility! Errgh, so >> frustrating!).
> Yes and no. For the user, aggregate initialization can be an > advantage in certain cases, e.g. my examples of letting the > compiler calculate array size. For the user, there are really > three things which interesting:
> 1. Aggregate initialization: useful for letting the compiler > calculate the size of an array, and in general for static > data.
> 2. Static initialization, for avoiding order of initialization > issues. This requires trivial constructors and constant > expressions in the initializer; for compound types (struct's > and arrays), the type must be an aggregate, and aggregate > initialization must be used. (Otherwise, you must have a > constructor somewhere, and the type ceases to be trivial.)
> 3. PODs or layout compatibility: mainly important with regards > to communicating with other languages, especially C. (The > system API is generally defined in terms of C these days.)
What about cross-platform interoperability? Write a struct here, read it there?
>>>> I think POD may be the key thing for layout compatibility >>>> with C and probably other languages. PODs no longer have to >>>> be aggregates in C++0x: they can have constructors, just >>>> not default or copy constructors, and no copy assignment >>>> operator. (N2690).
>>> Layout compatibility is an awkward problem. C++ can mandate >>> a certain number of things with regards to how the C++ >>> compiler lays out data, but it can't mandate anything with >>> regards to how other languages layout data. In the end, >>> it's a lot like the ``extern "C"'' fiasco: C++ requires a >>> compiler to support it, stating that functions declared >>> ``extern "C"'' must be callable from C (or something along >>> those lines). Which is all nice and fine, but what does it >>> mean if the platform doesn't have a C compiler? Or if it >>> has several C compilers, with different calling conventions?
>> "extern C" fiasco? News to me that it was a fiasco (you must >> be an implementor/insider, I bet)! I thought it was more like >> "thank god we can still use DLLs in C++".
> Fiasco may be too strong a word, but formally, the standard > guarantees much less than it seems to. (I certainly doesn't > guarantee anything with regards to DLLs, for example.)
I does indirectly. "C-linkage" (is that the right terminology?) is all that can be exported from DLLs ("sorry" to be so Windows-ish). I guess you probably could get all that name-mangled stuff to come out of a DLL on a single machine. You won't be selling that app to other people though, that's for sure.
>All that > it says (with regards to C) is ``Every implementation shall > provide for linkage to functions written in the C programming > language, "C", and linkage to C + + functions, "C++".'' Except > that it doesn't specify how these "functions written in the C > programming language" are to be compiled or linked; an > implementation may require you to compile them using a special C > compiler, which generates code incompatible with the system API, > for example. And it doesn't address the issue of what to do if > there is no C compiler for the system.
Are you being too hypothetical? I don't give it a second thought: I KNOW that I'll always be able to call "extern C" functions in a DLL (after LoadLibrary(), blah, blah.)
> At least some of the people involved with the standardization > proceedure are aware of this weakness, although the committee > doesn't seem to have wanted to address it. I think the general > intent is more along the lines that IF there is at least one C > implementation available on the platform, then the compiler must > support linkage with one of them, and document which one, and > what is necessary to make it work.
I seem to have missed "the weakness". I'm sure there is one if you say so. Anyway, I feel like "extern C" and "layout" are separate. It's all good information though.
> The probable reason the committee didn't address the problem is > that it isn't one in practice.
YES! Thanks for letting me know I'm not "out of it" (a bit insecure maybe, "out of it", no way!).
> Practically all platforms that > support C++ have a standard C ABI,
I didn't know that. Well maybe I sorta did because I rely on it ("extern C", "POD"). So there is a formality like the C++ ABI for Itanium for C?
> which is adhered to by all C > compilers, and practically all C++ compilers come with a C > compiler, and require no special steps to link C and C++. So > the standard may not say exactly what was wanted, but in > practice, everything works as was desired.
Interesting. Big kudos for C. But it is much easier in C to make a std ABI than in C++. C++ should have specified one from the beginning, but too late for that now. Live and learn.
> Until the day someone decides that C is dead enough that they > don't need a C compiler for their platform.
C/Std ABI: 1 point. C++/No Std ABI: -1 point. C++ is keeping C alive!
> [...] >>> If you look at it closely, you'll see that the standard >>> doesn't actually give any guarantees with regards to >>> standard layout and other languages, for the reason stated >>> above.
>> 'Care to restate that reason?
> The C++ standard can't impose anything on other languages, only > on C++.
k.
>>> There may be some advanced programming techniques which >>> depend on standard layout, but for the everyday user, the >>> only really significant distinction is whether the class >>> could be written in C or not
>> You meant if a class could look like a struct to C, surely.
> More or less, yes. With the addition of non-virtual member > functions, but that's about it.
k.
>>> ---if it could, it will be accessible from C, and probably >>> from most other languages as well (on typical small and >>> medium general purpose computers
>> That covers a lot (the most of it?) of ground, and propably >> shouldn't be flattened.
> Typical small and medium general purpose computers represent but > a small percentage of all computers.
And I know that too. I think in terms of the desktop/server space mostly as those are the applications I am building. I wasn't thinking "what pie piece of all computers", but rather "the desktop/server space is billions and billions of dollars of space" (with apologies to Carl Sagan).
> I'd guess off hand that > something like 90% of all computers are embedded systems. At > the other end, and this is the place where I suspect most of the > problems come, are the mainframes. IBM System z doesn't define > everything in terms of C, at least under the traditional OS's. > (You can also get it with Linux.) Cobol is still the > predominant language there.
I would wager that a poll (eww.. not one of THOSE!) would show that most readers of this ng are in the client-server (includes all things web etc. too) space. That is, working on software that interacts with humans (rather than controlling anti-lock brakes, etc). (Or I am a fish out of water?).
>>> ---I wouldn't count on it on mainframes, nor for that matter >>> on embedded systems); otherwise, it won't be. (You may, of >>> course, add non-virtual member functions, including >>> conversion operators, but not constructors, destructors or >>> assignment operators, without causing problems.)
>> I'm still hoping that Mr. Coffin was right about "convenience >> constructors" being OK. (Else I'll have to research and find >> out why there cannot be such. I'll blindly accept the >> concrete "special functions" as being special and reserved, >> but I really would want to know why "convenience constructors" >> are a no-go, if indeed so).
> You can't add "convenience constructors" today, and I'm sure > that Jerry didn't say that.
YOU said "today". The thread is all about C++0x. Indeed he did say that, but not with your "today" qualifier. I'm 99.9% sure that he is correct too.
> The next version of the standard > will allow it, I think, but only if you explicitly say you want > the "trivial" default constructor.
That's what he restated, but the thread was about C++0x, so you are sort of "preaching to the choir".
> And while initialization > syntax has been somewhat unified, I still don't think you can > get all of the features of aggregate initialization (especially > static initialization) if you provide any constructor; at most, > you'll be guaranteed a C compatible layout (but that's typically > the case today, with most compilers).
I assume that too today: that I can write "convenience constructors" and not have a worry. I just don't do it because it's not official.
>>> The other thing that is often important is whether the class >>> is an aggregate which supports static initialization. But >>> in practice, the two overlap; there are very few cases where >>> you can use static aggregate initialization but couldn't >>> write the class in C. (The presence of a pointer to member >>> in the class would be an example of one.)
>> I should have stopped responding to your post probably after I >> asked whether you meant the current standard or the yet-to-be >> (draft) C++. All of a sudden, I feel like I know NOTHING! >> Errrgh!! I think my house may explode if I start up Visual C++ >> and _I_ use it! I saw no red sticker on the box.. I got it for >> free as a download! ;)
> Unless I explicitly state otherwise, I'm talking about the > current standard.
Well, and again, the thread is specifically about C++0x. Did you miss that key aspect?
James Kanze wrote: > On Oct 31, 4:19 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: > [...] >>>> I downloaded N2960. I like to think in terms of the things >>>> a POD can or cannot have rather than the lingo like: >>>> trivially copyable, trivial class, standard layout, and on >>>> and on. In another post I wrote my understanding of what is >>>> and isn't allowed.
>>> The problem is that you can't express the requirements in >>> terms of can or cannot have.
>> Why is that? Is it so absolutely, or just because we are >> talking about C++?
> It's because the actual requirements contain several "must > have", not can have or cannot have.
While very abstract this subthread portion seems, you seem to be saying: "yes, you're right, so you're wrong". Let me clarify: I said I can think in simple terms but not or can't in C++ because C++ has to be like a president/politician walking the fence trying to be all things to all people and I live in Greenbough Alabama and just need a new ping pong paddle. In short, I'd MUCH rather have a language tool that I could compare against my checkoffs (can/cannot haves) rather than have to spend oodles of time deciphering terms like "trivial constructor" and the complex interplay between all the other 1250 pages of the standard. I was just explaining what I said, but suddenly, I feel catharted!
>>> At least partially, you have to express them in terms of >>> "must have": a POD must have a trivial default constructor, >>> for example (which is not the same thing as not having a >>> non-trivial default constructor---you have three >>> possibilities: no default constructor, trivial default >>> constructor and non-trivial default constructor).
>> But by "requirements", you mean "required by an >> implementation", yes?
> No. I mean the requirements on a class for it to be a POD.
k. I'm not sure from where in your other post I quoted "requirements".
James Kanze wrote: > On Oct 31, 4:25 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: >>> On Oct 29, 4:23 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote: >>>> In article <VV%Fm.41268$EU5.38...@newsfe05.iad>, >>>> spambus...@prodigy.net says...
> [...] >>> Attention: the requirement isn't that the class not have a >>> non-trivial X; it is that it have a trivial X. Thus, for >>> example:
>>> struct S { S( int ); int i; };
>>> doesn't have a non-trivial default constructor, but it >>> doesn't have a trivial one either, and thus, is not a POD.
>> Is it still layout-compatible with C though?
> In practice, with most compilers, yes.
I've been way to meek about using the guarantees given by my chosen compiler. More and more, I find myself at MSDN as my source for C++ information. What I find there is guaranteed to work because that's the compiler I'm using. C++ isn't losing ground, it's lost the war? Has most value in the Smithsonian?
> The current standard doesn't talk about "layout-compatible",
The current standard is off-topic in this thread.
> and > no C++ standard can impose anything on the C compiler. I didn't > see anything in N2914 (the latest draft that I happen to have > handy) that guaranteed that a "standard-layout" class is in > anyway compatible with C.
Hmm. I thought that was at least part of the point behind "standard layout". But, from a purely terminological point of view, it would seem to be ripe for bandaiding the lack of standard C++ ABI. A stepping stone for the original oversight.
> On the other hand, the whole concept of "layout-compatible" > seems to have been lifted from the C standard, and from a QoI > point of view, I would expect that anything with > "standard-layout" be compatible with C if the system defines a > standard C ABI (as most do).
Any guarantee is better than no guarantee. Even Master C++er Bjarne Stroupstrup acknowledged this point-of-quality (though somewhat condescendingly) in a presentation he gave (available on UTube).
>> (I'm not sure of the usefullness of "POD" anymore).
> Per se, they don't have much use.
I'd say (assertively) that they do, but I'm still struggling with the definition of such a thing.
> They do restrict the > implementation in some ways, however, that typically allows them > to be used in mixed language headers (headers which are used by > both C and C++).
>>> IIUC, in the next version of the standard, you will be able >>> to write:
>>> struct S { S( int ); S() = default; int i; };
>>> and it will have the required trivial default constructor.
>> And what will the compiler do with such a trivial default >> constructor?
> Nothing. Otherwise, the constructor wouldn't be trivial.
>> Why does it need to enslave that thing?
> I'm not sure what you're trying to ask there, but if it is "why > do we need a special syntax for this?", it's because the current > standard says that if a class has any constructor, the compiler > won't provide a default constructor implicitly, and a lot of > code counts on this.
I was just wondering why the compiler needed control of that special function. What book did I not buy or decide not to buy because I don't think that as an application programmer I need to worry about stuff that my employer calls "get up to speed on your technical skills on your own time so you can bring direct/real value to the company via purposeful software applications"?
On Nov 6, 11:21 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote:
> In article <1c83cc8c-9e7a-457a-bf85- > cfd3c93ad...@b15g2000yqd.googlegroups.com>, james.ka...@gmail.com > says... > [ ... ] > > It's not quite that bad; you don't need active cooperation > > with the C compiler. You do need a C compiler, however, and > > you need to know what it does and generates in order to make > > ``extern "C"'' work in C++. > I was thinking primarily of the fact that anytime the C > compiler changes anything about its ABI, the C++ compiler > needs to know about it and take steps to compensate. > Fortunately, at least in most cases the ABI is fairly stable, > so this doesn't arise a lot in practice.
Or that there are two different C compilers on the system, and they use different ABI's. Here, too, the case should be fairly rare, due to the fact that most OS's today define their interface in terms of C.
> [ ... ] > > One interesting idea that I've never seen done would be to > > conditionally add convenience functions in the header, something > > like: > > struct Toto > > { > > // ... > > #ifdef __cplusplus > > void someFunction() ; > > #endif > > }; > > In practice, I'm sure that this will work, but formally... > In practice, it's likely to work at least as long as none of > the functions is virtual. A virtual function would stand a > good chance of causing breakage though...
It would almost certainly break something.
> [ ... ] > > Just curious, but what effect does this have on static > > initialization using the agglomerate syntax. Can I still > > write something like: > > static X const table[] = { 1, 2, 3 }; > > and be guaranteed that the initialization precedes all code > > that I've written (including code in constructors of static > > objects)? > I haven't studied that in a lot of detail yet, but it looks > like there's a fair bit of new material to study.
Yes. And for various reasons, I've not been able to study much in the last year or so,
On Nov 7, 6:18 am, "dragan" <spambus...@prodigy.net> wrote:
> James Kanze wrote: > > On Oct 31, 4:12 am, "dragan" <spambus...@prodigy.net> wrote: > >> James Kanze wrote: > >>> On Oct 29, 11:40 pm, "dragan" <spambus...@prodigy.net> wrote:
[...]
> What about cross-platform interoperability? Write a struct > here, read it there?
That generally doesn't work, regardless. After all, it doesn't work for int; how could it work for a struct which contains an int?
[...]
> >> "extern C" fiasco? News to me that it was a fiasco (you > >> must be an implementor/insider, I bet)! I thought it was > >> more like "thank god we can still use DLLs in C++". > > Fiasco may be too strong a word, but formally, the standard > > guarantees much less than it seems to. (I certainly doesn't > > guarantee anything with regards to DLLs, for example.) > I does indirectly. "C-linkage" (is that the right > terminology?) is all that can be exported from DLLs ("sorry" > to be so Windows-ish).
That's not true. I've used DLL's without any C linkage on at least three platforms: Solaris, Linux and Windows.
> I guess you probably could get all that name-mangled stuff to > come out of a DLL on a single machine. You won't be selling > that app to other people though, that's for sure.
The only time name mangling is relevant is when the user explicitly loads a DLL and requests the function name (dlsym under Unix). In such cases, the usual solution is to have a single factory function as entry point, and declare that (and only that) as extern "C".
Of course, you can only load DLL's which are binary compatible. Which means a lot of different things, on different platforms.
> > All that it says (with regards to C) is ``Every > > implementation shall provide for linkage to functions > > written in the C programming language, "C", and linkage to C > > + + functions, "C++".'' Except that it doesn't specify how > > these "functions written in the C programming language" are > > to be compiled or linked; an implementation may require you > > to compile them using a special C compiler, which generates > > code incompatible with the system API, for example. And it > > doesn't address the issue of what to do if there is no C > > compiler for the system. > Are you being too hypothetical? I don't give it a second > thought: I KNOW that I'll always be able to call "extern C" > functions in a DLL (after LoadLibrary(), blah, blah.)
If you're talking about the standard, you have to consider all possible cases. I explicitly stated elsewhere that this isn't a problem in practice.
Of course, if you're calling LoadLibrary, then you're 100% Windows anyway, so you can count on the guarantees Microsoft gives as well as those in the standard.
> > At least some of the people involved with the > > standardization proceedure are aware of this weakness, > > although the committee doesn't seem to have wanted to > > address it. I think the general intent is more along the > > lines that IF there is at least one C implementation > > available on the platform, then the compiler must support > > linkage with one of them, and document which one, and what > > is necessary to make it work. > I seem to have missed "the weakness". I'm sure there is one if > you say so. Anyway, I feel like "extern C" and "layout" are > separate. It's all good information though.
The weakness is that for a C++ compiler to compile something which can be called from C, it needs a C compiler and some collaboration on the part of the C compiler. And the C++ standard has no influence over C compilers.
And extern "C" and layout are pretty orthogonal; depending on what you're doing, you might need both extern "C" and some sort of layout compatibility, however.
> > The probable reason the committee didn't address the problem > > is that it isn't one in practice. > YES! Thanks for letting me know I'm not "out of it" (a bit > insecure maybe, "out of it", no way!). > > Practically all platforms that support C++ have a standard C > > ABI, > I didn't know that. Well maybe I sorta did because I rely on > it ("extern C", "POD"). So there is a formality like the C++ > ABI for Itanium for C?
It depends on the platform, but for at least Posix and Windows, there has to be, since the system ABI is defined in terms of C. In practice, given the simplicity of C, most of the layout issues depend directly on the hardware---I don't need to read the compiler specifications for an IBM mainframe, for example, to know the layout, since a compiler isn't going to introduce unnecessary padding (it can, but it won't), and the hardware determines where the padding, etc., is necessary.
C++ is more complicated, since you have to consider things like how vtables are layed out. And for both C and C++, the calling conventions can vary. I don't know the situation on modern mainframes, but a long time ago, I know that different C compilers for the Siemens BS2000 used different calling conventions.
> > which is adhered to by all C compilers, and practically all > > C++ compilers come with a C compiler, and require no special > > steps to link C and C++. So the standard may not say > > exactly what was wanted, but in practice, everything works > > as was desired. > Interesting. Big kudos for C. But it is much easier in C to > make a std ABI than in C++. C++ should have specified one from > the beginning, but too late for that now. Live and learn.
The language specification cannot specify a standard ABI. That has to be hardware specific. Historically, C++ became significant after most hardware architectures had been specified, and there were several different C++ compilers around before C++ became important enough. The Itanium is the rare exception of an architecture which was defined after C++ was important, but before any compilers existed for it.
> > Until the day someone decides that C is dead enough that > > they don't need a C compiler for their platform. > C/Std ABI: 1 point. C++/No Std ABI: -1 point. C++ is keeping C > alive!
History is keeping C alive.
> > [...] > > Unless I explicitly state otherwise, I'm talking about the > > current standard. > Well, and again, the thread is specifically about C++0x. Did > you miss that key aspect?
Yes. Generally speaking, this newsgroup is about programming in C++; there is a separate group, comp.std.c++ for discussions of the standard. And while the separation isn't absolute, you can't program in C++0x today, so most discussion of it probably would be more appropriate in csc++.
> > There are no implementations of the next standard (can't be, > > since it doesn't exist yet), and the way things are going, > > I'm beginning to wonder if there will be any in my lifetime. > Now THAT is an interesting tangent. I was thinking that C++0x > features (at least a few stocking-stuffers) would be in my > favorite compiler for Xmas!
That is, of course, completely impossible, since the standard still hasn't been approved, and in fact, we still don't know exactly what will be in it. Generally, it takes a few years after the finalization of a standard for implementations to catch up; for that matter, most compilers today don't implement all of C++03.
> > With regards to Visual C++, it's a concrete implementation; > > concrete implementations always give you a lot more > > guarantees than the standard gives. > What do you mean by "concrete implementation"?
That it's real. It exists. It's not just an abstract specification.
> Did you just mean one specific implementation?
Yes. (I suppose that technically, it's several implementations, since you can control some of the aspects, like the signedness of a plain char, from the command line.)
> As opposed to worrying about all compilers or the majority or > average of them across all platforms and domains? I just have > some Windows apps to write.
If all you're targetting is Windows, then all you need to know is Visual C++.
> James Kanze wrote: > > On Oct 31, 4:25 am, "dragan" <spambus...@prodigy.net> wrote: > >> James Kanze wrote: > >>> On Oct 29, 4:23 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote: > >>>> In article <VV%Fm.41268$EU5.38...@newsfe05.iad>, > >>>> spambus...@prodigy.net says... > > [...] > >>> Attention: the requirement isn't that the class not have a > >>> non-trivial X; it is that it have a trivial X. Thus, for > >>> example: > >>> struct S { S( int ); int i; }; > >>> doesn't have a non-trivial default constructor, but it > >>> doesn't have a trivial one either, and thus, is not a POD. > >> Is it still layout-compatible with C though? > > In practice, with most compilers, yes. > I've been way to meek about using the guarantees given by my > chosen compiler. More and more, I find myself at MSDN as my > source for C++ information. What I find there is guaranteed to > work because that's the compiler I'm using. C++ isn't losing > ground, it's lost the war? Has most value in the Smithsonian?
I don't follow you. One of the reasons (not the only one) C++ continues to be important is because it leaves significant liberty to the implementation. It can be implemented on just about every platform.
> > The current standard doesn't talk about "layout-compatible", > The current standard is off-topic in this thread.
Some abstract future standard is arguably off-topic in this newsgroup. At least, there's a more appropriate news group for it: comp.std.c++.
> > and no C++ standard can impose anything on the C compiler. > > I didn't see anything in N2914 (the latest draft that I > > happen to have handy) that guaranteed that a > > "standard-layout" class is in anyway compatible with C. > Hmm. I thought that was at least part of the point behind > "standard layout".
Sort of. I suspect that the intent behind "standard-layout" does have to do with C compatibility. But the standard can't impose that, because compatibility is a two way street, and the C++ standard cannot impose anything on C. In practice, I think the intent is clear, and if an implementation provides both a C and a C++ compiler (the usual case when C++ is present), then I would expect, from a QoI point of view, that a standard-layout class be compatible with C, provided that it only uses elements of C (i.e. no pointers to members).
> But, from a purely terminological point of view, it would seem > to be ripe for bandaiding the lack of standard C++ ABI. A > stepping stone for the original oversight.
It would be nice if some architectures did define a standard C++ ABI. But it's up to the architectures; the C++ standard can't do it.
> > On the other hand, the whole concept of "layout-compatible" > > seems to have been lifted from the C standard, and from a > > QoI point of view, I would expect that anything with > > "standard-layout" be compatible with C if the system defines > > a standard C ABI (as most do). > Any guarantee is better than no guarantee. Even Master C++er > Bjarne Stroupstrup acknowledged this point-of-quality (though > somewhat condescendingly) in a presentation he gave (available > on UTube).
A standard can't guarantee a usable implementation. It's never more than part of what you count on.
> >> (I'm not sure of the usefullness of "POD" anymore). > > Per se, they don't have much use. > I'd say (assertively) that they do, but I'm still struggling > with the definition of such a thing.
Per se, limited strictly to the guaranteed in the standard, they don't. What they do is...
> > They do restrict the implementation in some ways, however, > > that typically allows them to be used in mixed language > > headers (headers which are used by both C and C++).
So in practice, they end up having a utility beyond that specified in the standard.
[...]
> > I'm not sure what you're trying to ask there, but if it is "why > > do we need a special syntax for this?", it's because the current > > standard says that if a class has any constructor, the compiler > > won't provide a default constructor implicitly, and a lot of > > code counts on this. > I was just wondering why the compiler needed control of that > special function.
I'm not too sure what you mean by "control of that special function". In C, it's possible to write something like:
struct S { int a; int b; }; S s;
and it was desired that this be possible in C++ as well, for reasons of C compatibility, if nothing else. This means that the compiler must implicitly declare and define a default constructor, if the user doesn't. It was also felt that if the user did define a constructor, it should be impossible to bypass it. This gives you the rules of the present standard.
James Kanze wrote: > On Nov 7, 6:53 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: >>> On Oct 31, 4:25 am, "dragan" <spambus...@prodigy.net> wrote: >>>> James Kanze wrote: >>>>> On Oct 29, 4:23 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote: >>>>>> In article <VV%Fm.41268$EU5.38...@newsfe05.iad>, >>>>>> spambus...@prodigy.net says...
>>> [...] >>>>> Attention: the requirement isn't that the class not have a >>>>> non-trivial X; it is that it have a trivial X. Thus, for >>>>> example:
>>>>> struct S { S( int ); int i; };
>>>>> doesn't have a non-trivial default constructor, but it >>>>> doesn't have a trivial one either, and thus, is not a POD.
>>>> Is it still layout-compatible with C though?
>>> In practice, with most compilers, yes.
>> I've been way to meek about using the guarantees given by my >> chosen compiler. More and more, I find myself at MSDN as my >> source for C++ information. What I find there is guaranteed to >> work because that's the compiler I'm using. C++ isn't losing >> ground, it's lost the war? Has most value in the Smithsonian?
> I don't follow you. One of the reasons (not the only one) C++ > continues to be important is because it leaves significant > liberty to the implementation. It can be implemented on just > about every platform.
That is not important.
>>> The current standard doesn't talk about "layout-compatible",
>> The current standard is off-topic in this thread.
> Some abstract future standard is arguably off-topic in this > newsgroup. At least, there's a more appropriate news group for > it: comp.std.c++.
That's your OPINION. (Or your attempt at imposition).
>>> and no C++ standard can impose anything on the C compiler. >>> I didn't see anything in N2914 (the latest draft that I >>> happen to have handy) that guaranteed that a >>> "standard-layout" class is in anyway compatible with C.
>> Hmm. I thought that was at least part of the point behind >> "standard layout".
> Sort of. I suspect that the intent behind "standard-layout" > does have to do with C compatibility. But the standard can't > impose that, because compatibility is a two way street, and the > C++ standard cannot impose anything on C. In practice, I think > the intent is clear, and if an implementation provides both a C > and a C++ compiler (the usual case when C++ is present), then I > would expect, from a QoI point of view, that a standard-layout > class be compatible with C, provided that it only uses elements > of C (i.e. no pointers to members).
You said: C++ is dead.
>> But, from a purely terminological point of view, it would seem >> to be ripe for bandaiding the lack of standard C++ ABI. A >> stepping stone for the original oversight.
> It would be nice if some architectures did define a standard C++ > ABI. But it's up to the architectures; the C++ standard can't > do it.
Hello. Bottleneck imposing itself .
>>> On the other hand, the whole concept of "layout-compatible" >>> seems to have been lifted from the C standard, and from a >>> QoI point of view, I would expect that anything with >>> "standard-layout" be compatible with C if the system defines >>> a standard C ABI (as most do).
>> Any guarantee is better than no guarantee. Even Master C++er >> Bjarne Stroupstrup acknowledged this point-of-quality (though >> somewhat condescendingly) in a presentation he gave (available >> on UTube).
> A standard can't guarantee a usable implementation. It's never > more than part of what you count on.
"If you're stupid, you vote".
>>>> (I'm not sure of the usefullness of "POD" anymore).
>>> Per se, they don't have much use.
>> I'd say (assertively) that they do, but I'm still struggling >> with the definition of such a thing.
> Per se, limited strictly to the guaranteed in the standard, they > don't. What they do is...
>>> They do restrict the implementation in some ways, however, >>> that typically allows them to be used in mixed language >>> headers (headers which are used by both C and C++).
> So in practice, they end up having a utility beyond that > specified in the standard.
> [...] >>> I'm not sure what you're trying to ask there, but if it is "why >>> do we need a special syntax for this?", it's because the current >>> standard says that if a class has any constructor, the compiler >>> won't provide a default constructor implicitly, and a lot of >>> code counts on this.
>> I was just wondering why the compiler needed control of that >> special function.
> I'm not too sure what you mean by "control of that special > function". In C, it's possible to write something like:
> struct S { int a; int b; }; > S s;
> and it was desired that this be possible in C++ as well, for > reasons of C compatibility, if nothing else. This means that > the compiler must implicitly declare and define a default > constructor, if the user doesn't. It was also felt that if the > user did define a constructor, it should be impossible to bypass > it. This gives you the rules of the present standard.
I don't believe you. I live in Romania and know your weak presentations.
On Nov 9, 8:21 am, "dragan" <spambus...@prodigy.net> wrote:
> James Kanze wrote: > > On Nov 7, 6:53 am, "dragan" <spambus...@prodigy.net> wrote: > >> James Kanze wrote: > >>> On Oct 31, 4:25 am, "dragan" <spambus...@prodigy.net> wrote: > >>>> James Kanze wrote: > >>>>> On Oct 29, 4:23 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote: > >>>>>> In article <VV%Fm.41268$EU5.38...@newsfe05.iad>, > >>>>>> spambus...@prodigy.net says... > >>> [...] > > I don't follow you. One of the reasons (not the only one) > > C++ continues to be important is because it leaves > > significant liberty to the implementation. It can be > > implemented on just about every platform. > That is not important.
The fact that C++ can be implemented on just about every platform is important to the majority of the committee. Some people don't care about anything but Windows, but they're far from a majority.
> >>> The current standard doesn't talk about "layout-compatible", > >> The current standard is off-topic in this thread. > > Some abstract future standard is arguably off-topic in this > > newsgroup. At least, there's a more appropriate news group > > for it: comp.std.c++. > That's your OPINION. (Or your attempt at imposition).
It's not an absolute, and some discussion of the future standard is certainly acceptable (since the future standard also concerns C++). But in general, people who want to discuss purely standard issues (and anything to do with the future standard is purely a standard issue, since it is pretty much irrelevant to programming today) do so in the group which is specialized for it: comp.std.c++.
> >>> and no C++ standard can impose anything on the C compiler. > >>> I didn't see anything in N2914 (the latest draft that I > >>> happen to have handy) that guaranteed that a > >>> "standard-layout" class is in anyway compatible with C. > >> Hmm. I thought that was at least part of the point behind > >> "standard layout". > > Sort of. I suspect that the intent behind "standard-layout" > > does have to do with C compatibility. But the standard > > can't impose that, because compatibility is a two way > > street, and the C++ standard cannot impose anything on C. > > In practice, I think the intent is clear, and if an > > implementation provides both a C and a C++ compiler (the > > usual case when C++ is present), then I would expect, from a > > QoI point of view, that a standard-layout class be > > compatible with C, provided that it only uses elements of C > > (i.e. no pointers to members). > You said: C++ is dead.
When did I ever say that? Just the contrary, C++ is a lot more alive than many people want.
> >> But, from a purely terminological point of view, it would > >> seem to be ripe for bandaiding the lack of standard C++ > >> ABI. A stepping stone for the original oversight. > > It would be nice if some architectures did define a standard C++ > > ABI. But it's up to the architectures; the C++ standard can't > > do it. > Hello. Bottleneck imposing itself .
In what sense? It's just common sense: a standard designed to be implemented on many different platforms can't impose anything which has to be specific to a given platform.
> >>> On the other hand, the whole concept of > >>> "layout-compatible" seems to have been lifted from the C > >>> standard, and from a QoI point of view, I would expect > >>> that anything with "standard-layout" be compatible with C > >>> if the system defines a standard C ABI (as most do). > >> Any guarantee is better than no guarantee. Even Master > >> C++er Bjarne Stroupstrup acknowledged this point-of-quality > >> (though somewhat condescendingly) in a presentation he gave > >> (available on UTube). > > A standard can't guarantee a usable implementation. It's > > never more than part of what you count on. > "If you're stupid, you vote".
You're not making sense.
> >>>> (I'm not sure of the usefullness of "POD" anymore). > >>> Per se, they don't have much use. > >> I'd say (assertively) that they do, but I'm still struggling > >> with the definition of such a thing. > > Per se, limited strictly to the guaranteed in the standard, they > > don't. What they do is... > What do they do? Hmm?
What I explained immediately following the "Per se, they don't have much use." Which still immediately follows.
> >>> They do restrict the implementation in some ways, however, > >>> that typically allows them to be used in mixed language > >>> headers (headers which are used by both C and C++). > > So in practice, they end up having a utility beyond that > > specified in the standard. > > [...] > >>> I'm not sure what you're trying to ask there, but if it is > >>> "why do we need a special syntax for this?", it's because > >>> the current standard says that if a class has any > >>> constructor, the compiler won't provide a default > >>> constructor implicitly, and a lot of code counts on this. > >> I was just wondering why the compiler needed control of that > >> special function. > > I'm not too sure what you mean by "control of that special > > function". In C, it's possible to write something like: > > struct S { int a; int b; }; > > S s; > > and it was desired that this be possible in C++ as well, for > > reasons of C compatibility, if nothing else. This means > > that the compiler must implicitly declare and define a > > default constructor, if the user doesn't. It was also felt > > that if the user did define a constructor, it should be > > impossible to bypass it. This gives you the rules of the > > present standard. > I don't believe you.
So read Stroustrup's D&E. Those are exactly the reasons (somewhat summarized) he gives.
> I live in Romania and know your weak presentations.
What does living in Romania have to do with anything? Except maybe that English isn't your first language, so you misunderstand some of the finer points, or misexpress what you are trying to say---but overall, your English seems quite good? And I don't know what you mean by "weak presentations", either. I'm just presenting the facts as I know them. There's no effort on my part to make a particular "presentation".
James Kanze wrote: > On Nov 9, 8:21 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: >>> On Nov 7, 6:53 am, "dragan" <spambus...@prodigy.net> wrote: >>>> James Kanze wrote: >>>>> On Oct 31, 4:25 am, "dragan" <spambus...@prodigy.net> wrote: >>>>>> James Kanze wrote: >>>>>>> On Oct 29, 4:23 pm, Jerry Coffin <jerryvcof...@yahoo.com> wrote: >>>>>>>> In article <VV%Fm.41268$EU5.38...@newsfe05.iad>, >>>>>>>> spambus...@prodigy.net says...
>>>>> [...] >>> I don't follow you. One of the reasons (not the only one) >>> C++ continues to be important is because it leaves >>> significant liberty to the implementation. It can be >>> implemented on just about every platform.
>> That is not important.
> The fact that C++ can be implemented on just about every > platform is important to the majority of the committee. Some > people don't care about anything but Windows, but they're far > from a majority.
"Oopsies" then, I must be autistic: I thought the world revolved around Windows! I mean, it's EVERYwhere: desktop, server, mobile, embedded. What more is there? Is anything more ubiquitous than Windows? Why bother with anything else? Learn one thing and be done with it, right? So what if every stoplight has QNX controlling it? Soon it will be Windows Embedded.
>>>>> The current standard doesn't talk about "layout-compatible",
>>>> The current standard is off-topic in this thread.
>>> Some abstract future standard is arguably off-topic in this >>> newsgroup. At least, there's a more appropriate news group >>> for it: comp.std.c++.
>> That's your OPINION. (Or your attempt at imposition).
> It's not an absolute, and some discussion of the future standard > is certainly acceptable (since the future standard also concerns > C++). But in general, people who want to discuss purely > standard issues (and anything to do with the future standard is > purely a standard issue, since it is pretty much irrelevant to > programming today) do so in the group which is specialized for > it: comp.std.c++.
Easy solution for those who don't want to discuss such things: change the channel (don't view the thread)! Right?
>>>>> and no C++ standard can impose anything on the C compiler. >>>>> I didn't see anything in N2914 (the latest draft that I >>>>> happen to have handy) that guaranteed that a >>>>> "standard-layout" class is in anyway compatible with C.
>>>> Hmm. I thought that was at least part of the point behind >>>> "standard layout".
>>> Sort of. I suspect that the intent behind "standard-layout" >>> does have to do with C compatibility. But the standard >>> can't impose that, because compatibility is a two way >>> street, and the C++ standard cannot impose anything on C. >>> In practice, I think the intent is clear, and if an >>> implementation provides both a C and a C++ compiler (the >>> usual case when C++ is present), then I would expect, from a >>> QoI point of view, that a standard-layout class be >>> compatible with C, provided that it only uses elements of C >>> (i.e. no pointers to members).
>> You said: C++ is dead.
> When did I ever say that? Just the contrary, C++ is a lot more > alive than many people want.
In looking to forget it's lineage but still purporting something like that. You can't have it both ways. And when is this next standard going to be real anyway? It needs to happen EVERY year or "yer (C++) outta here!". IMHO, of course.
>>>> But, from a purely terminological point of view, it would >>>> seem to be ripe for bandaiding the lack of standard C++ >>>> ABI. A stepping stone for the original oversight.
>>> It would be nice if some architectures did define a standard C++ >>> ABI. But it's up to the architectures; the C++ standard can't >>> do it.
>> Hello. Bottleneck imposing itself .
> In what sense? It's just common sense: a standard designed to > be implemented on many different platforms can't impose anything > which has to be specific to a given platform.
"Bottlenecks" are those things that cue other things behind them because they move too slowly: they impede progresss. Parallel paths are prudent and C++ needs to be "forked" or something (like in open source development): the backwards-compatible path (which will die off sooner than you think once the other paths open) and the path going forward. I said that quite well, actually, if I do say so myself. Kudos to MEEEE! :)
>>>>> On the other hand, the whole concept of >>>>> "layout-compatible" seems to have been lifted from the C >>>>> standard, and from a QoI point of view, I would expect >>>>> that anything with "standard-layout" be compatible with C >>>>> if the system defines a standard C ABI (as most do).
>>>> Any guarantee is better than no guarantee. Even Master >>>> C++er Bjarne Stroupstrup acknowledged this point-of-quality >>>> (though somewhat condescendingly) in a presentation he gave >>>> (available on UTube).
>>> A standard can't guarantee a usable implementation. It's >>> never more than part of what you count on.
>> "If you're stupid, you vote".
> You're not making sense.
It was a spoof on "designed by comittee". I think "the comittee" needs direction.
>>>>>> (I'm not sure of the usefullness of "POD" anymore).
>>>>> Per se, they don't have much use.
>>>> I'd say (assertively) that they do, but I'm still struggling >>>> with the definition of such a thing.
>>> Per se, limited strictly to the guaranteed in the standard, they >>> don't. What they do is...
>> What do they do? Hmm?
> What I explained immediately following the "Per se, they don't > have much use." Which still immediately follows.
And that's why the comittee and standard are undergoing so much revision on the issue? Maybe I just know what I read and it is not current about what's going on with the holy standard, but I do know that I read similar "sentiments" to mine that make your quip "they don't have much use", well, hogwash.
>>>>> They do restrict the implementation in some ways, however, >>>>> that typically allows them to be used in mixed language >>>>> headers (headers which are used by both C and C++).
>>> So in practice, they end up having a utility beyond that >>> specified in the standard.
>>> [...] >>>>> I'm not sure what you're trying to ask there, but if it is >>>>> "why do we need a special syntax for this?", it's because >>>>> the current standard says that if a class has any >>>>> constructor, the compiler won't provide a default >>>>> constructor implicitly, and a lot of code counts on this.
>>>> I was just wondering why the compiler needed control of that >>>> special function.
>>> I'm not too sure what you mean by "control of that special >>> function". In C, it's possible to write something like:
>>> struct S { int a; int b; }; >>> S s;
>>> and it was desired that this be possible in C++ as well, for >>> reasons of C compatibility, if nothing else. This means >>> that the compiler must implicitly declare and define a >>> default constructor, if the user doesn't. It was also felt >>> that if the user did define a constructor, it should be >>> impossible to bypass it. This gives you the rules of the >>> present standard.
>> I don't believe you.
> So read Stroustrup's D&E. Those are exactly the reasons > (somewhat summarized) he gives.
I was just maybe getting tired after your previous hogwash statement... "I don't believe you" follows directly: try to fool me once, shame on you. (Try to fool my twice, shame on me).
>> I live in Romania and know your weak presentations.
> What does living in Romania have to do with anything?
I don't really live there. I'm from there.
> Except > maybe that English isn't your first language,
Not hardly, but I think I do pretty well with it because I read other people's posts and can't decipher them for go to the bank!
> so you > misunderstand some of the finer points, or misexpress what you > are trying to say---but overall, your English seems quite good?
I speak better in English than what I learned as an elephant. I find English quite less demanding: know "rolling rrrrr's" and such. Spelling is pretty hard though, but I on purpose don't use a spell checker because I don't want people to think I am someone who I am not.
> And I don't know what you mean by "weak presentations", either. > I'm just presenting the facts as I know them. There's no effort > on my part to make a particular "presentation".
I have been following your posts that are in a topic that I find interesting and you seem to have a pattern. That pattern makes me think that you are "defender of C++" or "guaranteeing your job". ?
> James Kanze wrote: > > On Nov 9, 8:21 am, "dragan" <spambus...@prodigy.net> wrote: > >>>>> [...] > >>> I don't follow you. One of the reasons (not the only one) > >>> C++ continues to be important is because it leaves > >>> significant liberty to the implementation. It can be > >>> implemented on just about every platform. > >> That is not important. > > The fact that C++ can be implemented on just about every > > platform is important to the majority of the committee. > > Some people don't care about anything but Windows, but > > they're far from a majority. > "Oopsies" then, I must be autistic: I thought the world > revolved around Windows! I mean, it's EVERYwhere: desktop, > server, mobile, embedded. What more is there? Is anything more > ubiquitous than Windows? Why bother with anything else? Learn > one thing and be done with it, right? So what if every > stoplight has QNX controlling it? Soon it will be Windows > Embedded.
Windows is inappropriate for most applications, and most uses. Most embedded systems require real-time behavior, for example, which Windows doesn't provide. Most mainframes require a lot of functionality that Windows doesn't provide (and run on platforms that Windows doesn't support). Most large scale servers require more reliability and scalability than Windows provides.
Windows is far from ubiquitous. It's not even the most wide-spread OS. (VxWorks probably takes that prize.)
[...]
> >> You said: C++ is dead. > > When did I ever say that? Just the contrary, C++ is a lot > > more alive than many people want. > In looking to forget it's lineage but still purporting > something like that.
Bullshit. I never forgot C++'s lineage.
> You can't have it both ways. And when is this next standard > going to be real anyway?
Maybe never, the way things are going. Certainly not in the next few years.
> It needs to happen EVERY year or "yer (C++) outta here!". > IMHO, of course.
I agree that it needs to happen, and that the fact that it isn't happening is seriously hurting C++. But that doesn't change the fact that at present, it isn't happening, at least not too quickly.
[...]
> I have been following your posts that are in a topic that I > find interesting and you seem to have a pattern. That pattern > makes me think that you are "defender of C++" or "guaranteeing > your job". ?
You loose. I'm a professional, trying to get a job done. With tools that I stand a chance of seeing.
James Kanze wrote: > On Nov 15, 5:50 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: >>> On Nov 9, 8:21 am, "dragan" <spambus...@prodigy.net> wrote: >>>>>>> [...] >>>>> I don't follow you. One of the reasons (not the only one) >>>>> C++ continues to be important is because it leaves >>>>> significant liberty to the implementation. It can be >>>>> implemented on just about every platform.
>>>> That is not important.
>>> The fact that C++ can be implemented on just about every >>> platform is important to the majority of the committee. >>> Some people don't care about anything but Windows, but >>> they're far from a majority.
>> "Oopsies" then, I must be autistic: I thought the world >> revolved around Windows! I mean, it's EVERYwhere: desktop, >> server, mobile, embedded. What more is there? Is anything more >> ubiquitous than Windows? Why bother with anything else? Learn >> one thing and be done with it, right? So what if every >> stoplight has QNX controlling it? Soon it will be Windows >> Embedded.
> Windows is inappropriate for most applications, and most uses. > Most embedded systems require real-time behavior, for example, > which Windows doesn't provide.
Soon it will of course and now there are 3rd parties giving that.
> Most mainframes
There are still some of those? Go figure.
> require a lot of > functionality that Windows doesn't provide (and run on platforms > that Windows doesn't support).
Just a matter of time.
> Most large scale servers require > more reliability and scalability than Windows provides.
Just a matter of time.
> Windows is far from ubiquitous.
I beg to differ: life beyond me/us will be all "Windows". It is inevitable.
> It's not even the most > wide-spread OS. (VxWorks probably takes that prize.)
Windows has won. There soon will be nothing else. Anyone chasing anything else is a fool.
> [...] >>>> You said: C++ is dead.
>>> When did I ever say that? Just the contrary, C++ is a lot >>> more alive than many people want.
>> In looking to forget it's lineage but still purporting >> something like that.
> Bullshit. I never forgot C++'s lineage.
I didn't say "you", I said "C++". C++ is mortaly wounded and maybe you along with it. (Or maybe someone may want their money back!).
>> You can't have it both ways. And when is this next standard >> going to be real anyway?
> Maybe never, the way things are going. Certainly not in the > next few years.
So, dead: C++ is dead. You said it, so let it be written.
>> It needs to happen EVERY year or "yer (C++) outta here!". >> IMHO, of course.
> I agree that it needs to happen, and that the fact that it isn't > happening is seriously hurting C++. But that doesn't change the > fact that at present, it isn't happening, at least not too > quickly.
Too late: it's dead (not that it should have lived forever). Reality bytes. (At best).
> [...] >> I have been following your posts that are in a topic that I >> find interesting and you seem to have a pattern. That pattern >> makes me think that you are "defender of C++" or "guaranteeing >> your job". ?
> You loose. I'm a professional, trying to get a job done. With > tools that I stand a chance of seeing.
OK. I'm not dissing the Unions. I don't want any part of that. Though I want you "in the trenches" to know that I've been there.
On Nov 15, 11:54 am, "dragan" <spambus...@prodigy.net> wrote:
> James Kanze wrote: > > Windows is inappropriate for most applications, and most > > uses. Most embedded systems require real-time behavior, for > > example, which Windows doesn't provide. > Soon it will of course and now there are 3rd parties giving > that.
Been hearing that for quite some years now. The basic structure of Windows (and Unix, for the most part) doesn't really lend itself to hard real-time; it's not something you can add on top.
> > Most mainframes > There are still some of those? Go figure.
A lot of applications need a bit more than a PC. Companies are still using computers to manage large sets of data.
> > require a lot of functionality that Windows doesn't provide > > (and run on platforms that Windows doesn't support). > Just a matter of time.
Like, a million years...
Actually, I'd say that the tendancy is going in the opposite direction. Most IT organizations are realizing that one size doesn't fit all, and that you don't necessarily want the same system handling your critical data as you do on the desktop.
> > Most large scale servers require more reliability and > > scalability than Windows provides. > Just a matter of time.
Reliability improves with time, that's certain, and modern Windows is really pretty stable (which wasn't the case with NT, for example). But the other systems are aging as well. Linux is becoming stable---it's already stable enough for a lot of applications---and it scales a lot better than Windows.
> > Windows is far from ubiquitous. > I beg to differ: life beyond me/us will be all "Windows". It > is inevitable.
Obviously, you don't live in the real world, or at least, you're not aware of what's going on around you.
> > It's not even the most wide-spread OS. (VxWorks probably > > takes that prize.) > Windows has won. There soon will be nothing else. Anyone > chasing anything else is a fool.
Anyone restricting his choices to just Windows is an amateur, who doesn't understand the real world.
> > [...] > >>>> You said: C++ is dead. > >>> When did I ever say that? Just the contrary, C++ is a lot > >>> more alive than many people want. > >> In looking to forget it's lineage but still purporting > >> something like that. > > Bullshit. I never forgot C++'s lineage. > I didn't say "you", I said "C++". C++ is mortaly wounded and > maybe you along with it. (Or maybe someone may want their > money back!).
Well, I know a lot more than just C++. And I agree that C++ is "wounded", in some ways. But not morally. If for no other reason than the fact that for most applications, there's really no competitor---about the only possible one would be Ada 95, and that doesn't seem to have caught on.
James Kanze wrote: > On Nov 15, 11:54 am, "dragan" <spambus...@prodigy.net> wrote: >> James Kanze wrote: >>> Windows is inappropriate for most applications, and most >>> uses. Most embedded systems require real-time behavior, for >>> example, which Windows doesn't provide.
>> Soon it will of course and now there are 3rd parties giving >> that.
> Been hearing that for quite some years now. The basic structure > of Windows (and Unix, for the most part) doesn't really lend > itself to hard real-time; it's not something you can add on top.
>>> Most mainframes
>> There are still some of those? Go figure.
> A lot of applications need a bit more than a PC. Companies are > still using computers to manage large sets of data.
>>> require a lot of functionality that Windows doesn't provide >>> (and run on platforms that Windows doesn't support).
>> Just a matter of time.
> Like, a million years...
No, like right now Mr. Union Man who doesn't no his ass from a hole in the ground.
> Actually, I'd say that the tendancy is going in the opposite > direction.
Of course you would, but are in denial.
> Most IT organizations are realizing that one size > doesn't fit all, and that you don't necessarily want the same > system handling your critical data as you do on the desktop.
But you assume gestapo "organization". (nuff said).
>>> Most large scale servers require more reliability and >>> scalability than Windows provides.
> Reliability improves with time, that's certain, and modern > Windows is really pretty stable (which wasn't the case with NT, > for example). But the other systems are aging as well. Linux > is becoming stable---it's already stable enough for a lot of > applications---and it scales a lot better than Windows.
>>> Windows is far from ubiquitous.
>> I beg to differ: life beyond me/us will be all "Windows". It >> is inevitable.
> Obviously, you don't live in the real world, or at least, you're > not aware of what's going on around you.
Apparently don't ( are you a criminal? ). I assure you I know. You want to blather more?
bring it?
>>> It's not even the most wide-spread OS. (VxWorks probably >>> takes that prize.)
>> Windows has won. There soon will be nothing else. Anyone >> chasing anything else is a fool.
> Anyone restricting his choices to just Windows is an amateur, > who doesn't understand the real world.
>>>>> When did I ever say that? Just the contrary, C++ is a lot >>>>> more alive than many people want.
>>>> In looking to forget it's lineage but still purporting >>>> something like that.
>>> Bullshit. I never forgot C++'s lineage.
>> I didn't say "you", I said "C++". C++ is mortaly wounded and >> maybe you along with it. (Or maybe someone may want their >> money back!).
> Well, I know a lot more than just C++. And I agree that C++ is > "wounded", in some ways. But not morally.
I said mortally, not morally.
> If for no other > reason than the fact that for most applications, there's really > no competitor---about the only possible one would be Ada 95, and > that doesn't seem to have caught on.
then I am sorry and did not mean to hurt you.. apparenly dying is easy, and apparently I doing that.
On Nov 16, 10:09 am, "dragan" <spambus...@prodigy.net> wrote:
> James Kanze wrote: > > On Nov 15, 11:54 am, "dragan" <spambus...@prodigy.net> wrote: > >> James Kanze wrote:
[...]
> >>> require a lot of functionality that Windows doesn't provide > >>> (and run on platforms that Windows doesn't support). > >> Just a matter of time. > > Like, a million years... > No, like right now Mr. Union Man who doesn't no his ass from a > hole in the ground.
Like I said, been hearing that for years now. Doesn't seem to be happening. If anything, with the Web, things are moving the other direction. (Google doesn't run on Windows.)
> > Actually, I'd say that the tendancy is going in the opposite > > direction. > Of course you would, but are in denial.
No, I work in the real world. I don't know of any reasonably large organization that is 100% Windows.
> > Most IT organizations are realizing that one size doesn't > > fit all, and that you don't necessarily want the same > > system handling your critical data as you do on the > > desktop. > But you assume gestapo "organization". (nuff said). > >>> Most large scale servers require more reliability and > >>> scalability than Windows provides. > I am against you.
Who cares? Facts are facts, and if you don't care to deal with them, that's your problem, not mine.
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