- :: scope resolution operator - 1 Update
- :: scope resolution operator - 4 Updates
- Compiler issues - 3 Updates
- bad_cast exception 2 - 2 Updates
- bad_cast exception? - 2 Updates
- What practice can get speed improvement in C++? - 10 Updates
- Elementary question on references. - 1 Update
- clang-tidy simplify-boolean-expr check now available - 1 Update
- Concrete classes considered harmful - 1 Update
| ram@zedat.fu-berlin.de (Stefan Ram): Jul 19 07:02PM >And what's C++ all about, if it's not about being pedantic? :) »I have never, ever, ever seen a great software developer who does not have amazing attention to detail.« http://www.softwarebyrob.com/articles/Personality_Traits_of_the_Best_Software_Developers.aspx Programming is about expressing your ideas so that other people can understand them, "Programming is understanding." - Kristen Nygaard "Any fool can write code that a computer can understand. Good programmers write code that humans can understand." - Martin Fowler This suggest that it is about using a language correctly. »I've found that some of the best [Software ]developers of all are English majors. They'll often graduate with no programming experience at all, and certainly without a clue about the difference between DRAM and EPROM. But they can write. That's the art of conveying information concisely and clearly. Software development and writing are both the art of knowing what you're going to do, and then lucidly expressing your ideas.« Paul Potts http://praisecurseandrecurse.blogspot.com/2007/03/english-majors-as-programmers.html »Besides a mathematical inclination, an exceptionally good mastery of one's native tongue is the most vital asset of a competent programmer.« Edsgar Dijkstra »While sloppy writing does not invariably mean sloppy thinking, we've generally found the correlation to be strong -- and we have no use for sloppy thinkers. If you can't yet write competently, learn to.« Eric Raymond http://www.catb.org/~esr/faqs/hacker-howto.html#skills4 »The narrative measures of conjunction use, event content, perspective shift, and mental state reference were significantly predictive of later Math scores.« http://www.arts.uwaterloo.ca/%7Edoneill/papers/Storytelling%20and%20math.pdf |
| Jorgen Grahn <grahn+nntp@snipabacken.se>: Jul 17 06:51PM On Fri, 2015-07-17, Doug Mika wrote: > class of vector<int> class? Is it? > Does anyone know of a easy to read and comprehensive introduction to > how/when/why to use the scope resolution operator? *Shrug* Call me lazy, but I use :: when I have to; when the compiler refuses to understand me if I don't. For vector<int>::const_iterator it's obvious that I have to; there is no all-purpose "const_iterator", and I'm not inside the implementation of vector<int>, so I have to be specific (or use "auto"). /Jorgen -- // Jorgen Grahn <grahn@ Oo o. . . \X/ snipabacken.se> O o . |
| Paavo Helde <myfirstname@osa.pri.ee>: Jul 17 02:16PM -0500 Doug Mika <dougmmika@gmail.com> wrote in > So what precisely is the line inside vector<T> > typedef ? const_iterator; http://www.learncpp.com/cpp-tutorial/46-typedefs/ |
| Louis Krupp <lkrupp@nospam.pssw.com.invalid>: Jul 19 04:49AM -0600 On Fri, 17 Jul 2015 09:52:11 -0700 (PDT), Doug Mika <dougmmika@gmail.com> wrote: .. snip .. >So it begs the question, when we write vector<int>::const_iterator myIterator >can I deduce from this that const_iterator is an inner class of vector<int> class? Is it? To be pedantic, it doesn't *beg* the question, it *raises* the question. Hopefully, this link is accessible without a New York Times subscription: http://afterdeadline.blogs.nytimes.com/2008/09/25/begging-the-question-again/ That links to this page, which might be helpful: http://begthequestion.info/ And what's C++ all about, if it's not about being pedantic? :) Louis |
| legalize+jeeves@mail.xmission.com (Richard): Jul 20 06:59PM [Please do not mail me a copy of your followup] Louis Krupp <lkrupp@nospam.pssw.com.invalid> spake the secret code >And what's C++ all about, if it's not about being pedantic? :) s/C++/comp.lang.c++/ and I'm in agreement. A tautology is a thing that is tautological. -- "The Direct3D Graphics Pipeline" free book <http://tinyurl.com/d3d-pipeline> The Computer Graphics Museum <http://computergraphicsmuseum.org> The Terminals Wiki <http://terminals.classiccmp.org> Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com> |
| doctor@doctor.nl2k.ab.ca (The Doctor): Jul 20 03:02PM Got a weird, maybe some gurus might be able to help me out. By mistake I tpe gmke -j . Gmake being gnu make. since then on one system, the C compiler has not beeing working properly. Test errors, programmes not seeing the correct data, socket not starting ... What can I do to rectify this situation? -- Member - Liberal International This is doctor@@nl2k.ab.ca Ici doctor@@nl2k.ab.ca God,Queen and country!Never Satan President Republic!Beware AntiChrist rising! http://www.fullyfollow.me/rootnl2k Look at Psalms 14 and 53 on Atheism Abuse a man unjustly, and you will make friends for him. -Edgar Watson Howe |
| James Kuyper <jameskuyper@verizon.net>: Jul 20 01:39PM -0400 On 07/20/2015 11:02 AM, The Doctor wrote: > Test errors, programmes not seeing the correct data, > socket not starting ... > What can I do to rectify this situation? The -j option should only directly affect the files created by the run of gmake where you used that option. The effect might propagate to other things that were built using one of those files. If you erase all such files, and start over again, any problem actually related to your use of the -j option should disappear. I strongly suspect that many, if not all, of the symptoms you describe had nothing to do with your use of the -j option - there's no obvious reason why they should. If I'm right about that, you can expect those symptoms to continue occurring until you track down and correct the actual cause of those problems. |
| Keith Thompson <kst-u@mib.org>: Jul 20 11:23AM -0700 > Got a weird, maybe some gurus might be able to help me out. > By mistake I tpe gmke -j . > Gmake being gnu make. I presume you mean that you typed "gmake -j". I don't usually complain about typos, but these make your question difficult to read. > Test errors, programmes not seeing the correct data, > socket not starting ... > What can I do to rectify this situation? The "make" command will execute whatever commands are specified in the default Makefile. Those commands will have whatever effect they would have if you typed them at a shell prompt. Without knowing what's in your Makefile, it's impossible to know what your "gmake -j" command has done. There's a convention for Makefiles to have a "clean" target which will remove any generated files. It's possible that typing "gmake clean" will undo whatever damage you've done. I accept no responsibility for any consequences, which again are entirely dependent on the contents of the Makefile. (The default makefile may or may not be called "Makefile". Consult the documentation for details.) -- Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst> Working, but not speaking, for JetHead Development, Inc. "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister" |
| Paavo Helde <myfirstname@osa.pri.ee>: Jul 17 01:56AM -0500 Doug Mika <dougmmika@gmail.com> wrote in > Why is the following a compile time error and not a bad_cast > exception: Because dynamic_cast is defined to work only on pointers and references. > ampersands (&) in > Derived& rd = dynamic_cast<Derived&>(b); > but why? Because dynamic_cast is defined to work only on pointers and references. |
| Paavo Helde <myfirstname@osa.pri.ee>: Jul 17 11:09AM -0500 Doug Mika <dougmmika@gmail.com> wrote in > So in the example that compiles, with ampersands, (I include the > example again below) why doesn't it simply return rd=nullptr, why does > it throw an exception. A reference cannot have nullptr value. > My question I guess is, when does dynamic cast > throw an exception and when does it return nullptr? It returns nullptr if this is possible, otherwise throws. |
| Paavo Helde <myfirstname@osa.pri.ee>: Jul 17 01:50AM -0500 Doug Mika <dougmmika@gmail.com> wrote in > Why doesn't the following program throw a bad_cast exception? How can > the cast possibly suceed? It does not succeed - the resulting pointer will be NULL. The bad_cast exception is thrown only when casting to a reference type. By using either a pointer or a reference type you decide whether you want an automatic exception or not. |
| Paavo Helde <myfirstname@osa.pri.ee>: Jul 17 11:06AM -0500 Doug Mika <dougmmika@gmail.com> wrote in > What do you mean by an automatic exception? bad_cast |
| Barry Schwarz <schwarzb@dqel.com>: Jul 14 05:23PM -0700 On Tue, 14 Jul 2015 16:53:30 -0700 (PDT), fl <rxjwg98@gmail.com> wrote: >Experience in C/C++ code optimization for speed improvement. >I can only get the following answers: >1. Use reference to replace a direct parameter in function call; Benefit is realized only when argument is a very large aggregate or function is called very frequently. >2. Use register for some frequent variables; Compiler is free to ignore suggested storage class. >3. Use assembly code to replace C code No longer C or C++ and a maintenance nightmare. >4. Unroll a loop(?) Is this practical if the iteration count is not constant. >What is your opinion to the question? The best way of improving speed is to select or design a speed efficient algorithm. For a trivial example, computing factorials will be faster in a loop than using recursion. -- Remove del for email |
| Victor Bazarov <v.bazarov@comcast.invalid>: Jul 14 08:29PM -0400 On 7/14/2015 7:53 PM, fl wrote: > I am given the following question: > Experience in C/C++ code optimization for speed improvement. That's not a question. AFAIK, a question starts with an auxiliary verb or with a special word like "where" or "who" or "what" or "how", and ends with a question mark ("?"). Here you have a directive or an incomplete sentence. > 3. Use assembly code to replace C code > 4. Unroll a loop(?) > What is your opinion to the question? My opinion is that the questioner doesn't know the subject. 0. There is no such thing as C/C++. As for the choices for optimizing the speed, 1 and 4 are viable. Using 'register' is but a hint to the compiler. Choice 3 seems nothing to do with C++ (the topic of this newsgroup). V -- I do not respond to top-posted replies, please don't ask |
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Jul 15 05:07AM +0200 On 15-Jul-15 1:53 AM, fl wrote: > I am given the following question: > Experience in C/C++ code optimization for speed improvement. I read that as, "list your experience with speed optimization for C and C++ code". > 3. Use assembly code to replace C code > 4. Unroll a loop(?) > What is your opinion to the question? First, it's about particular programming languages, so presumably if you have experience with MEASURING, which is the most important thing, then you are expected to relate something of how you did that differently for the two mentioned languages, than for some other possible languages. I think you would be expected to mention some common tools and approaches for this, such as profiler, Unix-land `time` command, instrumenting code with timers and logging, and just dead reckoning (which can tell you if other ways are necessary). Regarding timers it would be nice if you know about the very limited resolution of C library time in Windows, and knowing about higher resolution C++11 timers, and about Boost timers. Second, after measuring comes algorithmic considerations. Replacing an O(n^2) algorithm with an O(n) algorithm is common. E.g. I think it would count in a positive way if you mentioned how you once optimized some repeated string concatenation, perhaps in Java. Knowing about support for this in C++11 would be extra point. Third, simple mechanical optimizations like you mention above. But your point (2), "Use register for some frequent variables", would count NEGATIVELY if I were to evaluate the answer, unless this is about an application to become part of a compiler development team (for ordinary app code you should leave that to the compiler: forcing it you're likely to do worse). On the other hand, knowing that the "register" keyword was deprecated in C++11 would be positive. Cheers & hth., - Alf -- Using Thunderbird as Usenet client, Eternal September as NNTP server. |
| "Lőrinczy Zsigmond" <nospam@for.me>: Jul 15 06:38AM +0200 Forget it. 'Smart tricks' won't give you more than a few percent. Plus kindly remember: Premature optimization is the root of all evil |
| Paavo Helde <myfirstname@osa.pri.ee>: Jul 15 12:22AM -0500 fl <rxjwg98@gmail.com> wrote in news:aaa4556e-8239-412c-be9d-7308a1a2cbb6 > I am given the following question: > Experience in C/C++ code optimization for speed improvement. This is not a question. If this is a requirement for a new hire, then I would think this means the ability to run a profiler like valgrind+callgrind, ability to interpret results and ability to modify the code to get rid of bottlenecks found this way. hth Paavo |
| bartekltg <bartekltg@gmail.com>: Jul 15 03:10PM +0200 On 15.07.2015 02:23, Barry Schwarz wrote: >> 1. Use reference to replace a direct parameter in function call; > Benefit is realized only when argument is a very large aggregate or > function is called very frequently. T& and const T& is quite good habit. In most cases it will be used with containers. And if we use it for small types (for example because we write const T & in template, and then use if with 'int') compiler regardless will copy value. >> 2. Use register for some frequent variables; > Compiler is free to ignore suggested storage class. Even worse. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf D.2 register keyword [depr.register] 1 The use of the register keyword as a storage-class-specifier (7.1.1) is deprecated. > The best way of improving speed is to select or design a speed > efficient algorithm. For a trivial example, computing factorials will > be faster in a loop than using recursion. IMHO it shoud be threated as the same algorithm, just different execution. I think changing recursion to loops, aside from oblivious cases like factorial, is premature optimalization. And in simple cases it change nothing, compiler will change it for us: c++ code: int factorial (int x){ if (x>1) return x*factorial(x-1); else return x; } asm generated by gcc .type _Z9factoriali, @function _Z9factoriali: .LFB1879: .cfi_startproc cmpl $1, %edi jle .L50 movl $1, %edx .p2align 4,,10 .p2align 3 .L49: leal -1(%rdi), %eax imull %edi, %edx cmpl $1, %eax movl %eax, %edi jne .L49 .L48: imull %edx, %eax ret .L50: movl %edi, %eax movl $1, %edx jmp .L48 Just a simple loop;-) bartekltg |
| JiiPee <no@notvalid.com>: Jul 16 05:00AM +0100 On 15/07/2015 14:10, bartekltg wrote: > if (x>1) return x*factorial(x-1); > else return x; > } factorial maybe not the best example as I would do it using constexpr: constexpr long long fac(int k) { return (k == 0) ? 1 : k * fac(k - 1); } giving an instant answer (calculated compile time). |
| bartekltg <bartekltg@gmail.com>: Jul 16 01:23PM +0200 On 16.07.2015 06:00, JiiPee wrote: > return (k == 0) ? 1 : k * fac(k - 1); > } > giving an instant answer (calculated compile time). Sure... main(){ big_int x; cin>>c; cout<<fac(x); } ;-) Also, instead int we have for example arthmetic modulo 1 178 973 853, so x can be too bit to put every possible answer in a array. bartekltg |
| JiiPee <no@notvalid.com>: Jul 16 04:48PM +0100 On 16/07/2015 09:04, Öö Tiib wrote: > Even IEEE double precision can't contain 23! accurately and will > overflow at 171! so usefulness of factorial is rather narrowly > limited. I did not mean it to be perfectly done (just the idea), but you can easily change it to something like: constexpr long long unsafeFac(int k) { return (k == 0) ? 1 : k * fac(k - 1); } constexpr long long fac(int k) { return (k < 0 || k > 15) ?|||throw| |exception()| : unsafeFac(k); } Now it complains *compile* time the error (which is definitely better than a runtime version) if k is too big or too small. |
| JiiPee <no@notvalid.com>: Jul 16 04:52PM +0100 On 16/07/2015 16:48, JiiPee wrote: > { > return (k < 0 || k > 15) ?|||throw| |exception()| : unsafeFac(k); > } ups, letters messed up, should be: constexpr long long fac(int k) { return (k < 0 || k > 15) ? throw exception() : unsafeFac(k); } |
| Jorgen Grahn <grahn+nntp@snipabacken.se>: Jul 16 05:58PM On Tue, 2015-07-07, Alf P. Steinbach wrote: > In C++ a reference refers to the result of the evaluation of the > initializer expression. But (as I recall) due to a sloppy formulation of > the specification of an early version of the Algol language, [...] Etc. In C++ -- (and all real languages. except pure pre-processor languages like cpp[0]) -- expressions are evaluated where they are, in their current context. So "index" is 5, and "ref" is a reference to vec[5], whatever that is at that point in time. Like any other reference into a std::vector, it's vulnerable to invalidation, though. For example, if you add enough elements to "vec" to force it to reallocate itself, "ref" will point to something crazy and unpredictable. If you don't it's just a sane reference to vec[5]. /Jorgen [0] cpp and make are the only remaining languages with this property that I can think of. Maybe m4 as well. Too bad that one of them is embedded into every C and C++ compiler ... -- // Jorgen Grahn <grahn@ Oo o. . . \X/ snipabacken.se> O o . |
| legalize+jeeves@mail.xmission.com (Richard): Jul 16 04:57PM [Please do not mail me a copy of your followup] Hi, I've contributed a check to clang-tidy that simplifies statements involving boolean literals. The name of the check is simplify-boolean-expr. It is not enabled by default, so you must request this check to get fixes applied to your code by clang-tidy. This has been checked into the trunk of clang and I believe will be available only by compiling the clang-tools-extra subrepository of the clang/llvm tree. I've been trying to get clang-tidy included in the regular distribution, but it hasn't made it into all the packages yet AFAIK. So you'll need to compile it from source to use it. This isn't hard, but it is a fairly lengthy build. I believe this check is sufficiently robust that it should make no changes to your code that change the semantics of the code. I've run this on the clang and LLVM code bases and addressed issues and made improvements to correct and such problems encountered there. However, I would love for this check to be run on more code bases to check for any additional problems I might have missed. You can provide feedback directly to me by email or via the clang bug tracker. <https://llvm.org/bugs/> This check looks for boolean expressions involving boolean constants and simplifies them to use the appropriate boolean expression directly. Examples: `if (b == true)` becomes `if (b)` `if (b == false)` becomes `if (!b)` `if (b && true)` becomes `if (b)` `if (b && false)` becomes `if (false)` `if (b || true)` becomes `if (true)` `if (b || false)` becomes `if (b)` `e ? true : false` becomes `e` `e ? false : true` becomes `!e` `if (true) t(); else f();` becomes `t();` `if (false) t(); else f();` becomes `f();` `if (e) return true; else return false;` becomes `return e;` `if (e) return false; else return true;` becomes `return !e;` `if (e) b = true; else b = false;` becomes `b = e;` `if (e) b = false; else b = true;` becomes `b = !e;` `if (e) return true; return false;` becomes `return e;` `if (e) return false; return true;` becomes `return !e;` The resulting expression `e` is modified as follows: 1. Unnecessary parentheses around the expression are removed. 2. Negated applications of `!` are eliminated. 3. Negated applications of comparison operators are changed to use the opposite condition. 4. Implicit conversions of pointer to `bool` are replaced with explicit comparisons to `nullptr`. 5. Implicit casts to `bool` are replaced with explicit casts to `bool`. 6. Object expressions with `explicit operator bool` conversion operators are replaced with explicit casts to `bool`. Examples: 1. The ternary assignment `bool b = (i < 0) ? true : false;` has redundant parentheses and becomes `bool b = i < 0;`. 2. The conditional return `if (!b) return false; return true;` has an implied double negation and becomes `return b;`. 3. The conditional return `if (i < 0) return false; return true;` becomes `return i >= 0;`. The conditional return `if (i != 0) return false; return true;` becomes `return i == 0;`. 4. The conditional return `if (p) return true; return false;` has an implicit conversion of a pointer to `bool` and becomes `return p != nullptr;`. The ternary assignment `bool b = (i & 1) ? true : false;` has an implicit conversion of `i & 1` to `bool` and becomes `bool b = static_cast<bool>(i & 1);`. 5. The conditional return `if (i & 1) return true; else return false;` has an implicit conversion of an integer quantity `i & 1` to `bool` and becomes `return static_cast<bool>(i & 1);` 6. Given `struct X { explicit operator bool(); };`, and an instance `x` of `struct X`, the conditional return `if (x) return true; return false;` becomes `return static_cast<bool>(x);` When a conditional boolean return or assignment appears at the end of a chain of `if`, `else if` statements, the conditional statement is left unchanged unless the option `ChainedConditionalReturn` or `ChainedConditionalAssignment`, respectively, is specified as non-zero. The default value for both options is zero. -- "The Direct3D Graphics Pipeline" free book <http://tinyurl.com/d3d-pipeline> The Computer Graphics Museum <http://computergraphicsmuseum.org> The Terminals Wiki <http://terminals.classiccmp.org> Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com> |
| legalize+jeeves@mail.xmission.com (Richard): Jul 15 04:57PM [Please do not mail me a copy of your followup] Ian Collins <ian-news@hotmail.com> spake the secret code >That is one solution I have used in the past, however mocking them >required a lot less work - especially if the mocking framework generates >all of the code for you. Yeah, it's a judgment call. If you're using a handfull of functions from the Win32 API, then creating your own domain-specific wrapper around them can be easy. If you need to wrap hundreds of API calls from Win32 then you'll want something more automated. On the flip side, sometimes you end up with better architecture as a side benefit of creating the insulting domain specific layer. You end up with interfaces that more directly describe the specific services needed by your application. -- "The Direct3D Graphics Pipeline" free book <http://tinyurl.com/d3d-pipeline> The Computer Graphics Museum <http://computergraphicsmuseum.org> The Terminals Wiki <http://terminals.classiccmp.org> Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com> |
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