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Why no std::byte in qt?!!



  • Situation:
    For last 3 hours i tried to figure out whats wrong with my code which i successfully ported in Qt. Now i find reason - qt betrayed me.

    I brought my code from VS to Qt. I runned it, everything seems fine,no errors in compile/runtime but program did'nt succeed. Then for next 3 hours i was looking where i made a mistake and found it.

    In vs i had

    using namespace std;
    

    for nicer code. But in Qt i forgot about that. So, as i understand Qt have it's own, embedded 'byte' type. And when i tried add prefix to my code like 'std::byte' compiler tells me "byte is not part of standard library".

    Wut? And then i goes to description of type, found that this type comes from <cstddef> so i included it, but nothing changed, still have only wrong byte from qt which is different.

    Tried to replace with QByteArray, but ofcourse it not working. Because i need somehow to use proper one: https://en.cppreference.com/w/cpp/types/byte



  • @Engelard
    As far as I recall whether or not you have an std::byte type is dependent on your system and nothing to do with Qt.
    It just may or may not be defined in your machines standard library.
    BTW std::byte is a C++17 thing.


  • Qt Champions 2019

    @Engelard said in Why no std::byte in qt?!!:

    qt betrayed me

    Sorry, but before complaining about Qt you should check what std::byte actually is.
    As @kenchan said std::byte is part of C++ standard library (as everything in std namespace).
    Furthermore std::byte is part of C++17 standard, that means: you need a C++ compiler supporting C++17.
    See https://en.cppreference.com/w/cpp/types/byte
    What compiler do you use?
    This problem is completely unrelated to Qt.


  • Moderators

    @Engelard said in Why no std::byte in qt?!!:

    In vs i had

    using namespace std;
    

    for nicer code. But in Qt i forgot about that.

    And thats one of the reasons I don't use using namespace at least globaly for a class, one should always be certain what one is actually referencing/using

    That makes me also a non user of auto, if I can avoid it.



  • @jsulm said in Why no std::byte in qt?!!:

    This problem is completely unrelated to Qt.

    It works in VS, and not working in Qt. And you telling me that "completely unrelated"? How your argument should work?



  • @Engelard said in Why no std::byte in qt?!!:

    It works in VS, and not working in Qt. And you telling me that "completely unrelated"? How your argument should work?

    Well, Qt is no compiler... it's a framework. Therefore the argument holds.



  • @jsulm said in Why no std::byte in qt?!!:

    What compiler do you use?

    alt text



  • @JohanSolo said in Why no std::byte in qt?!!:

    Well, Qt is no compiler... it's a framework. Therefore the argument holds.

    I don't understand. Each IDA must have it's own compiler, no?



  • Just tell me what should i do to be able to use std::byte in qt...

    P.S. this topic for some reason became 'auto topic', but this keyword wont work for my case because it can't convert in proper 'raw byte' type because there is no such thing in my Qt(yet).



  • @Engelard
    No, the Qt IDE is not a compiler, it provides you with the ability to use whatever compiler you have installed and is compatible with the version of Qt you are using.
    In the case of the VS IDE it just happens to be provided by Microsoft and they also provide their own compiler as part of the package. That is just the way it is!

    If you want to use the c++17 features in Qt Creator you must tell the compiler you want to use it by putting CONFIG += c++17 in your pro file.
    EDIT:
    Another way to make it use the c++17 features is to add QMAKE_CXXFLAGS += -std:c++17 this should be equivalent to the above if you use the correct compiler.
    I think it will only work the the 15.0 compiler, I tried it with the 14.0 compiler and the complier did not like it. I don't use Qt with the 15.0 version yet so I can't test that.



  • @Engelard said in Why no std::byte in qt?!!:

    what should i do to be able to use std::byte in qt

    Just chose as a compiler VS 2017.3 [P2] or later (i.e. the compiler 15.0)

    Each IDA must have it's own compiler, no?

    Absolutely not.

    this topic for some reason became 'auto topic',

    Forked to https://forum.qt.io/topic/95412/rants-about-auto



  • @kenchan said in Why no std::byte in qt?!!:

    I think it will only work the the 15.0 compiler, I tried it with the 14.0 compiler and the complier did not like it. I don't use Qt with the 15.0 version yet so I can't test that.

    Did'nt work out((

    @VRonin said in Why no std::byte in qt?!!:

    Just chose as a compiler VS 2017.3 [P2] or later (i.e. the compiler 15.0)

    Which one should i choose?:

    alt text

    And then. Where and for what exactly file should i looking at? Can i add same compiler from my VS2017?



  • @Engelard said in Why no std::byte in qt?!!:

    Did'nt work out((

    What did you do?



  • @VRonin like @kenchan said, add in to .pro file one of these:

    CONFIG += c++17
    QMAKE_CXXFLAGS += -std:c++17
    

    Non of them worked. Still no byte type in std::



  • Can you show us what kit are you building with? see image below:
    0_1539108183391_Capture.png



  • @VRonin I just added first manual compiler, which from folder of my VS2017 Community, still it says that byte is not part of std.

    alt text

    Here it is:

    alt text

    Did i did that correct?



  • Oh and in the Kits i just now noticed, for some reason there is compilers for amd chosen, when i have normal for intel i suppose in my VS. And i can't change it, when i press manage - it's simply throw me in to compilers tab so i don't know how to change it:

    alt text

    AND. i just now added one more custom compiler, also from VS2017 but 64 version, since i have x64 CPU and windows, maybe should be proper one, am i right?

    alt text

    Only one thing (as i understand) left to do. Is apply compiler which i chose in 'compilers' tab, because there is still my old as you can see from screenshot

    alt text


  • Qt Champions 2019

    @Engelard "How your argument should work?" - easy. You should understand the difference between a compiler, an IDE and a framework. Qt is a C++ framework (not a compiler), QtCreator is an IDE which supports many different compilers, but does not contain own compilers. C++standard library (std::*) comes as part of the compiler and NOT Qt, that's why it is "completely unrelated to Qt". So, as already explained by others you need a compiler supporting C++2017 and activate C++2017 supports in the pro file (not sure it is needed with Microsoft compilers).

    Didn't QtCreator auto-detect your VS2017 compiler? Usually there is no need to configure compilers manually. The 15.0 is already the C++ compiler from VS2017, why do you add the compiler manually? Does it now work with your "Desktop Qt 5.10.1 MSVC2017 64bit2" Kit and autodetected VS2017 compiler?

    One note: an IDE does not have to contain any compilers. Microsoft Compilers can be installed and used without Visual Studio. The reasons are: it must be possible to use compilers without a huge IDE (for example in a continuous integration system) and many IDEs (like QtCreator) support different compilers which come from different companies or are open source. QtCreator, for example, supports Microsoft Compilers and MinGW on Windows. Qt Online Installer for Windows provides the possibility to install MinGW as it is Open Source. Microsoft compilers on the other hand can't be provided by Qt Online Installer as this not allowed by Microsoft.



  • @Engelard said in Why no std::byte in qt?!!:

    still it says that byte is not part of std.

    • Did you #include <cstddef>?
    • Can you open Visual Studio 2017, create a simple console program and test if it works there?

  • Qt Champions 2017

    @Engelard said in Why no std::byte in qt?!!:

    there is compilers for amd chosen, when i have normal for intel i suppose in my VS

    This is the CPU instruction set. Intel processors use amd64, so it's correct.


  • Moderators

    @Engelard said in Why no std::byte in qt?!!:

    CONFIG += c++17
    QMAKE_CXXFLAGS += -std:c++17

    Please try

    CONFIG +=c++1z

    This works for me with Visual Studio 2017 compiler.



  • @Engelard
    OK, problem solved...
    In spite the Microsoft docs which say the -std:c++17 flag can be used in VS2017 to enable the c++17 features it does not seem to work though the command line via qmake!
    but adding...
    DEFINES += _HAS_STD_BYTE
    and
    QMAKE_CXXFLAGS += -std:c++17
    to the pro file does work and I can use std::byte in the code.

    QMAKE_CXXFLAGS += -std:c++1z also worked

    I hope this works for you too.



  • @VRonin said in Why no std::byte in qt?!!:

    @Engelard said in Why no std::byte in qt?!!:

    still it says that byte is not part of std.

    • Did you #include <cstddef>?

    Yes, i mentioned in firsts posts.

    • Can you open Visual Studio 2017, create a simple console program and test if it works there?

    In first post i told that original program which widely using std::byte was from my VS2017(ofc it works).

    @kshegunov

    This is the CPU instruction set. Intel processors use amd64, so it's correct.

    lol



  • @kshegunov said in Why no std::byte in qt?!!:

    @Engelard said in Why no std::byte in qt?!!:

    there is compilers for amd chosen, when i have normal for intel i suppose in my VS

    This is the CPU instruction set. Intel processors use amd64, so it's correct.

    lol

    @kkoehne said in Why no std::byte in qt?!!:

    @Engelard said in Why no std::byte in qt?!!:

    CONFIG += c++17
    QMAKE_CXXFLAGS += -std:c++17

    Please try

    CONFIG +=c++1z

    This works for me with Visual Studio 2017 compiler.

    Sorry, no effect. Tried both of them, separately and together like in your message.



  • @kenchan damn it worked! At least now after typing std::b it advice me byte type and word now not dead black but violet like all valid variables should be(finally).

    But!)

    It still rejects to compile. I tried to clean all, then rebuild, but same error:

    alt text



  • Even restart of Qt don't help, what's wrong...



  • @Engelard
    hmm?? looks like you have another problem somewhere.
    Can you show us your pro file?
    Can you show us a screen shot of your kits panel for the kit you are currently using again please?
    Can you show us a screen shot the qt versions panel and the compilers panel again please?
    Can can you show a screen shot of the compiler output when you compile your code with the std::byte declaration please?

    Thank you



  • @Engelard
    I few tests show me that you can actually get away with using either DEFINES += _HAS_STD_BYTE or QMAKE_CXXFLAGS += -std:c++17 when using the VS 15.0 compiler.
    Using both is obviously twice as safe.

    Just make sure you blow away the build folder, rerun qmake and rebuild just to be sure.

    creating a new Non-Qt Plain C++ project with this pro file

     TEMPLATE = app
    CONFIG += console
    CONFIG -= app_bundle
    CONFIG -= qt
    DEFINES += _HAS_STD_BYTE
    QMAKE_CXXFLAGS += -std:c++17
     
    SOURCES += \
            main.cpp
    

    and this c++ code worked fine for me.

    #include <iostream>
    #include <cstddef>
     
    using namespace std;
     
    int main()
    {
        byte stdbyte;
        stdbyte = std::byte(0);
        byte *arr = new std::byte[2];
        arr[0] = std::byte(0x2a);
     
        cout << "Hello World!" << endl;
        return 0;
    }
    

    Why don't you try this and see if it works?



  • This post is deleted!


  • Seems the problem was in old build directory. After complete deletion of it - program finally compiles:

    alt text

    DAMN it was hard and so long. New features of new C++17 in Qt cost so much...



  • @Engelard
    Yes, that is what I suspected was the problem.
    Glad you finally got it working.


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