C++ Gurus

• 

  SOLVED connect is driving me batty!
  • fcarney  

  4
  0
  Votes
  4
  Posts
  32
  Views

  

  If you're using C++14 and a decent compiler you can shorten that a little to connect(socket, qOverload<QAbstractSocket::SocketError>(&QWebSocket::error), [=](QAbstractSocket::SocketError error){ }); which still kinda sucks. I hope we get rid of the existing overloads in Qt6. I sure would love to get rid of stuff like currentIndexChanged() overloaded on int and QString.
• 

  UNSOLVED A Makefile problem
  • mrdebug  

  27
  0
  Votes
  27
  Posts
  83
  Views

  

  @mrdebug said in A Makefile problem: After having studying how to QtCreator generates a Makefile, I have inserted the following lines on code in my Makefile Mmm, so are you editing the Makefile by hand? I'm not sure it's a good way to go. You may want to edit your Qt project file (.pro) and let qmake create your Makefile then, passing to it all your settings...
• 

  SOLVED How is this error possible? g++: error: build/.o: No such file or directory
  • fcarney  

  3
  0
  Votes
  3
  Posts
  31
  Views

  

  @fcarney said in How is this error possible? g++: error: build/.o: No such file or directory: is what caused this. is your issue solved then? If so please don't forget to mark your post as such. Thanks
• 

  UNSOLVED Difference in class size during Virtual inheritance
  • Vinoth Rajendran4  

  10
  0
  Votes
  10
  Posts
  187
  Views

  

  @kshegunov I'm not an expert on that but I do see boost when optimizing for reduced vtable usage, so either my hardware doesn't do that good of a job or something else is going on. Thanks for a nudge, I guess it's something worth looking into.
• 

  UNSOLVED C++ sensor gateway design problem.
  • GoRo3  

  4
  0
  Votes
  4
  Posts
  77
  Views

  

  Why not have a central where you collect the data and then have specific "propagetors" that will publish/send/whatever ? You'll keep your devices focused on getting data and then you can an new propagation channels San you see fit.
• 

  UNSOLVED Compile problem
  • Q139  

  3
  0
  Votes
  3
  Posts
  157
  Views

  

  Wonderful , also had some problems with using signals improperly.
• 

  SOLVED Polymorphism doesn't work with base class value member?
  • enjoysmath  

  3
  0
  Votes
  3
  Posts
  126
  Views

  

  Solution is to install MSVC 2017 for Qt5 kit, which I think has polymorphic_value capabilities now.
• 

  SOLVED Error while compiling Qt mySQL driver
  • denko  

  22
  0
  Votes
  22
  Posts
  13378
  Views

  

  @chrabaszcz-patryk Hi I had the same problem with qtsqldrivers-config.pri I leave it here, maybe it will be helpful Go to : /Qt_new/5.9.1/Src/qtbase/src/plugins/sqldrivers Run qmake: ../../../../../gcc_64/bin/qmake sqldrivers.pro After that I got: Configure summary: Qt Sql: DB2 (IBM) .............................. no InterBase .............................. no MySql .................................. yes OCI (Oracle) ........................... no ODBC ................................... no PostgreSQL ............................. no SQLite2 ................................ no SQLite ................................. yes Using system provided SQLite ......... no TDS (Sybase) ........................... no Then go to: /Qt_new/5.9.1/Src/qtbase/src/plugins/sqldrivers/mysql Run qmake again: ../../../../../../gcc_64/bin/qmake mysql.pro Run make: make You will see as a part of an output message that it was compiled and moved into: "mv -f libqsqlmysql.so ../plugins/sqldrivers/" I had this problem when added Qt 5.13.0 using online installation to the Qt 5.12 i have already installed i thought the installation was wrong until i came across your solution. Thanks you very much.
• 

  UNSOLVED How to use bit operations
  • K-Str  

  19
  0
  Votes
  19
  Posts
  621
  Views

  

  @aha_1980 Thank you for this tip. This means I have to implement a timer with a interval of 200µs which kicks off reading of one new bit from the RX868SH-DV. OK I will try it. And then I give you an answer. But now I got a new problem using timers in QT-Creator. I make a new topic for this. my new topic for two timer
• 

  SOLVED Can someone explain this syntax to me?
  • CynicalPenguin  

  5
  0
  Votes
  5
  Posts
  1268
  Views

  

  @jjlee said in Can someone explain this syntax to me?: the previous syntax doesn't seem to work anymore It does, but you need to tell the compiler which version you want to use. For that you can use https://doc.qt.io/qt-5/qtglobal.html#qOverload macro.
• 

  SOLVED implicit initialization
  • fcarney  

  3
  0
  Votes
  3
  Posts
  222
  Views

  

  One issue I ran into was my local variables were showing zeros as well. It wasn't until I inited the ram with 255 for every character and used new(mempool()) to use that preinited ram that I did see uninitialized ram. Of course that was on the heap and not the stack. I did test this over the weekend and observed what you said. Variables declared outside of local scope are initialized to zero. While stack and heap are not.
• 

  UNSOLVED C++ Improvement!
  c++ • • Arjunkumar  

  4
  0
  Votes
  4
  Posts
  285
  Views

  

  https://i.redd.it/1fl5yi6bbpzz.png
• 

  SOLVED strange hexadecimal representation
  • r3d9u11  

  8
  0
  Votes
  8
  Posts
  150
  Views

  

  thank to all for hints and clarifications!
• 

  SOLVED Casting covertus numberus?!
  • fcarney  

  11
  0
  Votes
  11
  Posts
  224
  Views

  

  @fcarney BTW, reading around (and then I must get back to my work!), it seems there is another C++ variant to int64_t(something) which is actually supposedly preferred (to just that one): int64_t{something}! From what I read, the consensus is best to use the static_cast<> family of casts for all of this. The basic claim is that it makes it easier to search source code for these.
• 

  SOLVED Prebuilt number range generators?
  • fcarney  

  9
  0
  Votes
  9
  Posts
  363
  Views

  

  @Konstantin-Tokarev said in Prebuilt number range generators?: irange Thanks for the irange suggestion: for(auto x: boost::irange(10,20)){ qInfo() << x; } out: 10 11 12 13 14 15 16 17 18 19
• 

  SOLVED Functional Programming in C++: Why?
  • fcarney  

  7
  0
  Votes
  7
  Posts
  606
  Views

  

  I have this book. I have read chapter 1. I was on the fence as to the value of FP. The first chapter definitely has concrete and relatable examples of how the FP approach can improve my code. It does not espouse the idea of only using FP, but a more pragmatic approach of balancing how you think about code. I like the idea of adding tools to my toolbox rather than upending how I write code altogether. The best way to describe the approach this book is taking so far is: thinking about the process versus thinking about the steps. It is very similar to process control in that respect. So its a refreshing way to model code. I expect good things in the next chapters.
• 

  SOLVED Which comparison loop is easier to reason about and read?
  • fcarney  

  7
  0
  Votes
  7
  Posts
  254
  Views

  

  @kshegunov It doesn't help that the OP's code uses std::all_of while his comment has "I like the idea of std::any_of".... Which is just as easy using your "old and tested way, which is rather simple and explicit": for (size_t i = 1, size = sequence.size(); i < size; i++) { if (board[sequence[0]] != board[sequence[i]]) return false; } return true;
• 

  SOLVED Why is Icon (enum) in QMessageBox have so strange form?
  • GRUB_666  

  5
  0
  Votes
  5
  Posts
  264
  Views

  

  At a glance verification of an enums value rather than counting lines. Saves coder time. One goal of good programming is being able to maintain code. So making it easier to troubleshoot a value quickly meets that requirement.
• 

  SOLVED Tieing the lifetime of an object to that of a lambda?
  • fcarney  

  5
  0
  Votes
  5
  Posts
  277
  Views

  

  @Kent-Dorfman said in Tieing the lifetime of an object to that of a lambda?: Personally I think lambdas are way too overused I think at this point I am more interested in the "neat" factor than the utility. I think it will be a nice tool to attach objects as needed to signals, or to graft simpler signals onto more complex outputs. I could imagine this being used as a generator of objects. Lambda capture also reminds me of RAII as used in objects. So the technical reason for now "cause its cools, and could be useful...maybe".
• 

  SOLVED Creating an enum like structure for data types other than integral?
  • fcarney  

  2
  0
  Votes
  2
  Posts
  170
  Views

  

  @fcarney said in Creating an enum like structure for data types other than integral?: Are there other, better ways to make enum like structures for data types other than integrals? Not really, but you can "improve" your struct based solution by making the members static: then you don't have to create an instance of the struct and you can do: Token::Invalid Also, since enum values cannot be changed you should make the struct elements const: struct Token{ static const QString Invalid; static const QString P1; static const QString P2; } const QString Token::Invalid = " "; const QString Token::P1 = "X"; const QString Token::P2 = "O";
• 

  UNSOLVED Can someone please help me on how to upgrade Qt libraries to latest version (4.5 to 5.12)
  • Chaitu247  

  7
  0
  Votes
  7
  Posts
  237
  Views

  

  @aha_1980 Thank you very much. I start working on that!!
• 

  SOLVED What does "control returns to the event loop of the receiver's thread" mean?
  • Factao  

  6
  0
  Votes
  6
  Posts
  467
  Views

  

  Ok, thank you all, you have answered my question. I guess this is time to read some documentation...
• 

  UNSOLVED Mac Stringstream returns wrong output
  c++ mac os qtcreator 4.9.1 stringstream • • Bugi  

  32
  0
  Votes
  32
  Posts
  1005
  Views

  

  @wraitii Thanks for information! You've probably meant libstdc++ and libc++, because libc is kinda different thing
• 

  SOLVED auto can create instances of private classes
  • fcarney  

  2
  0
  Votes
  2
  Posts
  147
  Views

  

  This feature allows to return values of "hidden" type from library which can be used only with auto or passed as an argument to some other library function. For example, standard library of C++17 introduces a concept of node handle, type of which is left as implementation detail and may be different between implementations or their versions. You can do a few operations with node handles, but cannot ever reference their "true" type.
• 

  SOLVED MySQL query
  • Xmodpt  

  11
  0
  Votes
  11
  Posts
  508
  Views

  

  @VRonin Hello m8 Thankyou verry much for all your help. ALL is working like it should thanks to you. Until next time Xmodpt
• 

  SOLVED compiler reports that Ui is an incomplete type
  • mzimmers  

  16
  0
  Votes
  16
  Posts
  423
  Views

  

  @kshegunov said in compiler reports that Ui is an incomplete type: error: allocation of incomplete type 'Ui::WifiSetup' This means the class declaration is not available. Troubleshoot as follows (skip steps that you've checked already): Make sure you include the generated header where you allocate. Make sure qmake's rerun Make sure the name of the widget in the designer matches the name of the class. Ding. It was #3, a result of my hasty editing in Designer. Thanks to all who looked at this.
• 

  UNSOLVED Delete unused c++ files from the project
  • rockon209  

  2
  0
  Votes
  2
  Posts
  143
  Views

  

  @rockon209 Please don't cross-post! Closing this one and leaving https://forum.qt.io/topic/103622/delete-unused-c-files-from-the-project open.
• 

  SOLVED QProcess not launching exe in Microsoft OneDrive directory
  • ktwalker  

  8
  0
  Votes
  8
  Posts
  381
  Views

  

  Folks, Thanks for the direction. The escape character for QStrings is \. So the solution is QString exeName = "\"" + dirName + "Program.exe\""; Kris
• 

  This topic is deleted!
  • hdfjgjsd03  

  1
  0
  Votes
  1
  Posts
  2
  Views

  No one has replied

• 

  This topic is deleted!
  • mzimmers  

  2
  0
  Votes
  2
  Posts
  6
  Views
• 

  SOLVED template/macro for reducing redundant functions?
  • fcarney  

  10
  0
  Votes
  10
  Posts
  405
  Views

  

  @fcarney said in template/macro for reducing redundant functions?: Okay, I think I get it. Partly. What a template is from the point of view of the binary is nothing - it does not produce anything. A template is way to tell your compiler to substitute template arguments at some point and produce a real living class (or function) which it then can compile to assembly. Instantiation happens on first use with a given set of template parameters ordinarily. In this case I "abuse" that peculiarity by saying: okay, there is a template function (the declaration) but when you need to substitute the types (i.e. instantiate the template on use) you can't, because you don't know the function body. The extern template at the end is to make all that at all useful - fine there's no body, so the template can't be instantiated in the user code, but I can give you some instantiations I made explicitly somewhere else (in this case in the source). So it works like this: The compiler sees there's a declaration. It also sees there are 2, 3, 4 instantiations that are done somewhere else (i.e. the declarations at the bottom). In the source it has the template body, and has been told to instantiate the template - that's fine, it can as it knows how. When you use it somewhere it matches the stuff that's declared (i.e. the template declaration and the instantiations) against what you request. It puts a reference for the linker to resolve. If there's an instantiation provided for the given set of template parameters, everything is fine - the linker's going to clean up the mess and link the function you have with the usage. If not, i.e. you used the template with a parameter that hand't been explicitly instantiated, then the linker complains - there's no such thing.
• 

  SOLVED Functor without warnings
  • casperbear  

  5
  0
  Votes
  5
  Posts
  323
  Views

  

  @Konstantin-Tokarev It worked. Thank you. I had been looking at that warning for months. Final solution didn't require to move pure virtual function's definition to *.cpp. I'll leave it here for future seekers. DLL *.pro DEFINES += APPLICATIONMODEL_LIBRARY DLL and EXE *.h #ifdef APPLICATIONMODEL_LIBRARY # define APPLICATIONMODEL_EXPORT Q_DECL_EXPORT #else # define APPLICATIONMODEL_EXPORT Q_DECL_IMPORT #endif DLL *.h class APPLICATIONMODEL_EXPORT CActionFunctor { public: virtual ~CActionFunctor(); virtual void operator()() = 0; }; template <typename TClass> class TActionFunctor : public CActionFunctor { public: TActionFunctor(TClass *object, void(TClass::*function)()) { Object = object; Function = function; } void operator()() { (*Object.*Function)(); } private: TClass *Object; void (TClass::*Function)(); }; DDL *.cpp CActionFunctor::~CActionFunctor() { } APPLICATIONMODEL_EXPORT CActionFunctor *SimulationInstanceChanged = nullptr; void CSimulation::Bind(CSimulation **simulation) { *simulation = this; (*SimulationInstanceChanged)(); } EXE *.cpp APPLICATIONMODEL_EXPORT CActionFunctor *SimulationInstanceChanged; WMain::WMain() { SimulationInstanceChanged = new TActionFunctor<WMain>(this, &WMain::OnSimulationInstanceChanged); }
• 

  SOLVED Warning: overrides a destructor but is not marked 'override'
  • saurabh162  

  11
  0
  Votes
  11
  Posts
  974
  Views

  

  Hello @JonB, @J-Hilk, @Konstantin-Tokarev, Once again thank you very much for your help. Now I have understood it correctly.
• 

  SOLVED Passing reference of class from call on class
  • fcarney  

  6
  0
  Votes
  6
  Posts
  325
  Views

  

  @kshegunov Well the use case was to match the interface currently being used to provide variables to the tr() (translate functions). We have code that looks like this: tr("Log Message","Status: %1").arg(2) Well the problem with this is the string is in a server and the client needs to translate the message. So I wanted to wrap the message in a similar way and use the same arg() interface we currently use. JMsg(QT_TRANSLATE_NOOP("Log Message","Hello: %1 %2 %3")).arg(1).arg("full").arg("world"); The JMsg overloads an operator: operator QString(){return toString();} This allows the call to be very similar to the original tr() call and return a string to the function it is created in. JMsg is intended to be a temporary variable. The string it produces is a JSON string that embeds the message with parameters and the args in a list. This is decoded by the client and translated using a function designed to interpret the JSON code. So effectively I am modeling it after how the translate parameter system works, for the API anyway. Not the underlying code. I don't program javascript or java much. Mainly C++ and Python.
• 

  SOLVED Containers with C++17 structured bindings
  • david_dlqa  

  13
  0
  Votes
  13
  Posts
  659
  Views

  

  @J.Hilk Thanks, that makes sense. I just copied that from the documentation hence I thought that was not a concern. I reran the tests and got almost the same results, so I think with times in the seconds, the qDebug overhead is not significant
• 

  SOLVED Signal/slot and const parameters
  • KroMignon  

  11
  0
  Votes
  11
  Posts
  659
  Views

  

  @VRonin said in Signal/slot and const parameters: Mixed feeling about this. Qt internally will const_cast the sender if the signal is const :O I had no idea.
• 

  UNSOLVED OpenCL won't run while debugging
  • beecksche  

  6
  0
  Votes
  6
  Posts
  367
  Views

  

  Both suggestions don't work. I don't think the code is incorrect, i found many other examples uses the same part of code. The docs also says, that the function will ignore the pointer if it's NULL. Unfortunetaly i'm not able to update my Intel Graphics Driver to the newest release. Maybe that's the reason. Nevertheless, I tried a lot of OpenCL kernels, which will work correctly in Release mode. I also can skip the exception in Debug mode by continue the debugging twice, and the functions return the correct result. In Visual Studio the same exception is caused in the ntdll.exe. But this is also not helpfull for me to find the problem. Keep searching.
• 

  SOLVED from int to double
  • A Former User  

  6
  0
  Votes
  6
  Posts
  466
  Views

  

  @J.Hilk thanks
• 

  SOLVED Creating call back functions for a library
  • Yaswanth  

  18
  0
  Votes
  18
  Posts
  764
  Views

  

  I could use member function of class as a callback. I have sent function object which is returned by std::bind to the library . In library used std::function to hold bind expression. So as per the data, respective callback functions can be called.
• 

  SOLVED Memory fragmentation
  • casperbear  

  13
  0
  Votes
  13
  Posts
  870
  Views

  

  @casperbear said in Memory fragmentation: Yeah, you caught me. I'm inclined to use heap because I'm primarily a C# developer. Sounds like I need to learn that move semantics after all, to use stack approach more effectively. free store memory management is a whole field of study unto itself, so yes...research research research. @kshegunov -- Well put. You saved me from posting what could have inadvertantly turned into a rant. LOL