C++ Gurus

• 

  Unsolved implicit initialization
  • fcarney

  2
  2
  Posts
  66
  Views

  

  @fcarney
  Yes, and also as per reading the link you referenced, your understanding is correct. Static/global storage declarations will be initialized to 0, but local/stack will be uninitialized. This would be just as true if your variable was int instead of struct ....

  I'm not sure why you cannot think how to test this. I have gone to http://cpp.sh and pasted:

  // Example program #include <iostream> #include <string> struct SomeStruct { int somevalue; } buncha_structs[256]; int main() { SomeStruct local_structs[256]; std::cout << local_structs[1].somevalue << std::endl; std::cout << buncha_structs[1].somevalue << std::endl; }

  available as http://cpp.sh/5gbae (don't know how long that link is valid).

  Note that I think you did not intend the typedef in your code. With the typedef, your buncha_structs is a type not a variable. I have removed the typedef to give you a global variable, which I think is what you intended.

  The above reliably outputs 0 for the second, global variable case, but outputs a "random", changing number each time for the first, local case. You should also see that it shows an "uninitialized" warning message against your use in the local variable case.

• 

  Unsolved C++ Improvement!
  c++ • • Arjunkumar

  4
  4
  Posts
  156
  Views

  

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

• 

  Solved strange hexadecimal representation
  • r3d9u11

  8
  8
  Posts
  52
  Views

  

  thank to all for hints and clarifications!

• 

  Solved Casting covertus numberus?!
  • fcarney

  11
  11
  Posts
  114
  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
  9
  Posts
  204
  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
  7
  Posts
  383
  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
  7
  Posts
  153
  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
  5
  Posts
  178
  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
  5
  Posts
  158
  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
  2
  Posts
  107
  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
  7
  Posts
  149
  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
  6
  Posts
  269
  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++ qtcreator 4.9.1 stringstream mac os • • Bugi

  32
  32
  Posts
  611
  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
  2
  Posts
  105
  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
  11
  Posts
  362
  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
  16
  Posts
  235
  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
  2
  Posts
  102
  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
  8
  Posts
  252
  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
  1
  Posts
  2
  Views

  No one has replied

• 

  This topic is deleted!
  • mzimmers

  2
  2
  Posts
  6
  Views
• 

  Solved template/macro for reducing redundant functions?
  • fcarney

  10
  10
  Posts
  256
  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
  5
  Posts
  215
  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
  11
  Posts
  432
  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
  6
  Posts
  241
  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
  13
  Posts
  420
  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
  11
  Posts
  351
  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
  6
  Posts
  261
  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
  • vale88

  6
  6
  Posts
  325
  Views

  

  @J.Hilk thanks

• 

  Solved Creating call back functions for a library
  • Yaswanth

  18
  18
  Posts
  534
  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
  13
  Posts
  626
  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

• 

  Solved prohibiting duplicate connections?
  • Kent-Dorfman

  10
  10
  Posts
  459
  Views

  

  At least not here, because we don't know the deep details.

  It's a twofold problem:

  The connect needs a context QObject, if not specified that's the sender.
  Then the question becomes is the following the same connection: QObject * otherObject; void freeFunction(); QObject::connect(this, &MyClass::someSignal, otherObject, freeFunction); QObject::connect(this, &MyClass::someSignal, this, freeFunction);

  where, conceivably, otherObject may be in a different thread. Nobody knows how these two should be distinguished exactly - in some cases they may be considered the same, in some they may not. freeFunction isn't attached to the class of this, nor to the class of otherObject.

  A functor (a.k.a. lamda, a.k.a. function object, std::function, etc.) more often than not has (internal) state. So two instances of the same type (i.e. two lambdas) can't be distinguished due to the fact that the state is not known to Qt. Example: auto functor1 = [this] () -> void { qDebug() << "Functor"; } auto functor2 = functor1; //< Object copy here! We are dealing with another entity entirely! QObject::connect(this, &MyClass::someSignal, this, functor1); QObject::connect(this, &MyClass::someSignal, this, functor2); //< functor2 isn't functor1

  And to add insult to injury:

  QObject::connect(this, &MyClass::someSignal, this, functor1); //< Object copy of functor1! QObject::connect(this, &MyClass::someSignal, this, functor1); //< Object copy of functor1, again!
• 

  Solved How does Qt::connectiontype work?
  • Factao

  5
  5
  Posts
  333
  Views

  

  Thank you!

• 

  Unsolved QPrint no possible to set page size and orientation (ubuntu 18.04)
  • gfxx

  11
  11
  Posts
  574
  Views

  

  Ran your code on:

  Ubuntu 18.04 64 bit Qt 5.12.2 gcc

  I get paper and orientation outputs consistent with my selections. I tried 3 variations.
  Edit:
  Output: print to pdf

• 

  Unsolved QImage from QDatastream of float values
  • connecting_dots

  4
  4
  Posts
  247
  Views

  

  What kind of images are that in the first place ?
  Where do they come from ?

• 

  Solved Violation of MISRA08_18-4-1
  • Phadnis

  6
  6
  Posts
  280
  Views

  

  @Kent-Dorfman Thanks I agree.

• 

  Solved Number Type Cast
  • beecksche

  21
  21
  Posts
  1271
  Views

  

  @jsulm , @SGaist

  thanks a lot. I thought I had understood the problem. But it seems to be a bit more complicated.

  Hopefully, in some time, I will understande when to use which cast explicitly and for what reason.

  Until thenI hope that these parts of the code don't make any trouble.

• 

  Solved Is there 'findChild<>()' but for simple variables?
  • Engelard

  6
  6
  Posts
  271
  Views

  

  the long and short of this issue is that if you want to "find" an object in Qt then you need that object ot be a sublclass of QObject. So, if you want to use it for ordinal/simple/immutable variables then you need to create special classes that wrap those variables and derive from QObject.

  HOWEVER!!!! trying to do this really deontes a poor design and you should reevaluate your reason for doing so.

• 

  Solved Qt with eclipse C++
  • GastonMelo

  6
  6
  Posts
  449
  Views

  

  When last I looked at the Qt plugin for eclipse it was hopelessly broken. At the time eclipse had a lot of problems parsing the Qt framework include files and MOC system for code checking. Are you using the plugin, or just using eclipse as an editor?

• 

  Solved "nested name specifier" error
  • mzimmers

  8
  8
  Posts
  570
  Views

  

  OK, thanks for the education...they're all removed and the warnings have disappeared.

• 

  Solved Question about QThread and how thread work in general.
  • Factao

  32
  32
  Posts
  1730
  Views

  

  Perhaps, but I don't see an implication for the case of signal-slot connections vs direct synchronization ... at the end of the day the former still uses a mutex to serialize access to the queued events ...