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Converting a QByteArray in Hexa format into an Int

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  • jsulmJ jsulm

    @Pantoufle https://doc.qt.io/qt-6/qbytearray.html#toInt
    with base = 16

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    Pantoufle
    wrote on last edited by
    #3

    @jsulm Doest seems to work, I tried with this code :

        ByteArray mydata = QByteArray::fromHex("00004A9E");
        bool ok;
        int a = mydata.toInt(&ok, 16);
        if(!ok)
            std::cout << "Fail convert" << std::endl;
    
        std::cout << "A TEST : " << a << std::endl;
    

    This code return a converting error

    jsulmJ 1 Reply Last reply
    0
    • P Pantoufle

      @jsulm Doest seems to work, I tried with this code :

          ByteArray mydata = QByteArray::fromHex("00004A9E");
          bool ok;
          int a = mydata.toInt(&ok, 16);
          if(!ok)
              std::cout << "Fail convert" << std::endl;
      
          std::cout << "A TEST : " << a << std::endl;
      

      This code return a converting error

      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by
      #4

      @Pantoufle You do not need fromHex...

      https://forum.qt.io/topic/113070/qt-code-of-conduct

      P 1 Reply Last reply
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      • jsulmJ jsulm

        @Pantoufle You do not need fromHex...

        P Offline
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        Pantoufle
        wrote on last edited by
        #5

        @jsulm

        Sorry, but this may lack some context. Actually, I don't really construct this QByteArray using "fromHex"; instead, I receive it through a serial connection and then store it in a QByteArray.

        In the example above, indeed, if I remove the "fromHex" part, it works, but then the QByteArray will be 8 bytes long, which is not my case. The data will be only 4 bytes, which corresponds to creating a QByteArray with "fromHex".

        M jsulmJ JonBJ 3 Replies Last reply
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        • P Pantoufle

          @jsulm

          Sorry, but this may lack some context. Actually, I don't really construct this QByteArray using "fromHex"; instead, I receive it through a serial connection and then store it in a QByteArray.

          In the example above, indeed, if I remove the "fromHex" part, it works, but then the QByteArray will be 8 bytes long, which is not my case. The data will be only 4 bytes, which corresponds to creating a QByteArray with "fromHex".

          M Offline
          M Offline
          mpergand
          wrote on last edited by
          #6

          @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

          but then the QByteArray will be 8 bytes long,

          Wrong, two hex digits = 1 byte.

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          • P Pantoufle

            @jsulm

            Sorry, but this may lack some context. Actually, I don't really construct this QByteArray using "fromHex"; instead, I receive it through a serial connection and then store it in a QByteArray.

            In the example above, indeed, if I remove the "fromHex" part, it works, but then the QByteArray will be 8 bytes long, which is not my case. The data will be only 4 bytes, which corresponds to creating a QByteArray with "fromHex".

            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #7

            @Pantoufle Sorry, I don't understand your problem. As @mpergand wrote two hex digids represent one byte. Did you actually try toInt? And are you sure that what you receive is actually hex encoded number-string? How exactly are those numbers sent?

            https://forum.qt.io/topic/113070/qt-code-of-conduct

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            • P Pantoufle

              @jsulm

              Sorry, but this may lack some context. Actually, I don't really construct this QByteArray using "fromHex"; instead, I receive it through a serial connection and then store it in a QByteArray.

              In the example above, indeed, if I remove the "fromHex" part, it works, but then the QByteArray will be 8 bytes long, which is not my case. The data will be only 4 bytes, which corresponds to creating a QByteArray with "fromHex".

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by JonB
              #8

              @Pantoufle
              Decide whether your input is:

              • 4 bytes of (binary) data, i.e. a binary representation of ant int, whether is low- or high-endian order; or
              • 8 hexadecimal characters to be converted to an int (presumably high-to-low).

              Then you/we will know what you're actually asking. Till then it is quite unclear, and only you know what your input is....

              1 Reply Last reply
              1
              • M mpergand

                @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

                but then the QByteArray will be 8 bytes long,

                Wrong, two hex digits = 1 byte.

                P Offline
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                Pantoufle
                wrote on last edited by
                #9

                @mpergand

                I know that two hex digits = 1 byte, therefore in my example if i remove the fromHex it create a 8 bytes QbyteArray :

                QByteArray mydata ="00004A9E";
                
                std::cout << "My data size : " << mydata.size() << std::endl;
                

                Output:

                My data size : 8
                

                Maybe i miss understood the "You don't need the fromHex" quote and I'm sorry if so.

                @JonB

                It's a 4 bytes if binary data representation of an int, high endian

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                • P Offline
                  P Offline
                  Pantoufle
                  wrote on last edited by
                  #10

                  I've found an answer that works :

                  QByteArray mydata = QByteArray::fromHex("00004A9E");
                  QDataStream ds(mydata);
                  ds.setByteOrder(QDataStream::BigEndian);
                  int mydataInteger;
                  ds >> mydataInteger;
                  std::cout << "Int content : " << mydataInteger << std::endl;
                  

                  But I would be glad if you can make me understand why toInt() don't work.

                  jsulmJ 1 Reply Last reply
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                  • P Pantoufle

                    I've found an answer that works :

                    QByteArray mydata = QByteArray::fromHex("00004A9E");
                    QDataStream ds(mydata);
                    ds.setByteOrder(QDataStream::BigEndian);
                    int mydataInteger;
                    ds >> mydataInteger;
                    std::cout << "Int content : " << mydataInteger << std::endl;
                    

                    But I would be glad if you can make me understand why toInt() don't work.

                    jsulmJ Offline
                    jsulmJ Offline
                    jsulm
                    Lifetime Qt Champion
                    wrote on last edited by
                    #11

                    @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

                    why toInt() don't work

                    This code prints 19102:

                    QByteArray n("00004A9E");
                    bool ok;
                    qDebug() << n.toInt(&ok, 16);
                    

                    https://forum.qt.io/topic/113070/qt-code-of-conduct

                    P 1 Reply Last reply
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                    • jsulmJ jsulm

                      @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

                      why toInt() don't work

                      This code prints 19102:

                      QByteArray n("00004A9E");
                      bool ok;
                      qDebug() << n.toInt(&ok, 16);
                      
                      P Offline
                      P Offline
                      Pantoufle
                      wrote on last edited by
                      #12

                      @jsulm

                      Yes but the code u just send is a 8 bytes QbyteArray :

                      QByteArray mydata("00004A9E");
                          std::cout << "My data : " << mydata.size() << std::endl;
                      
                          bool ok;
                          int a = mydata.toInt(&ok, 16);
                          if(!ok)
                              std::cout << "Fail convert" << std::endl;
                      
                          std::cout << "My data int " << a << std::endl;
                      
                      P J.HilkJ 2 Replies Last reply
                      0
                      • P Pantoufle

                        @jsulm

                        Yes but the code u just send is a 8 bytes QbyteArray :

                        QByteArray mydata("00004A9E");
                            std::cout << "My data : " << mydata.size() << std::endl;
                        
                            bool ok;
                            int a = mydata.toInt(&ok, 16);
                            if(!ok)
                                std::cout << "Fail convert" << std::endl;
                        
                            std::cout << "My data int " << a << std::endl;
                        
                        P Offline
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                        Pantoufle
                        wrote on last edited by
                        #13

                        @Pantoufle

                        Forgot the output :

                        My data : 8
                        My data int : 19102
                        
                        M 1 Reply Last reply
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                        • P Pantoufle

                          @Pantoufle

                          Forgot the output :

                          My data : 8
                          My data int : 19102
                          
                          M Offline
                          M Offline
                          mpergand
                          wrote on last edited by
                          #14

                          @Pantoufle
                          What is the format of the original data ?
                          ASCII in hex format ?
                          Binary in big endian ?
                          Other ?

                          P 1 Reply Last reply
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                          • P Pantoufle

                            @jsulm

                            Yes but the code u just send is a 8 bytes QbyteArray :

                            QByteArray mydata("00004A9E");
                                std::cout << "My data : " << mydata.size() << std::endl;
                            
                                bool ok;
                                int a = mydata.toInt(&ok, 16);
                                if(!ok)
                                    std::cout << "Fail convert" << std::endl;
                            
                                std::cout << "My data int " << a << std::endl;
                            
                            J.HilkJ Offline
                            J.HilkJ Offline
                            J.Hilk
                            Moderators
                            wrote on last edited by J.Hilk
                            #15

                            @Pantoufle this is probably through the ambiguity of the QByteArray constructor, wich builds down to char* or an other QByteArray

                            use the proper constructor from a String, and it should be fine:

                            auto mydata = QString("00004A9E").toLatin1();
                                std::cout << "My data : " << mydata.size() << std::endl;
                            
                                bool ok;
                                int a = mydata.toInt(&ok, 16);
                                if(!ok)
                                    std::cout << "Fail convert" << std::endl;
                            
                                std::cout << "My data int " << a << std::endl;
                            

                            Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


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                            A: It's blue light.
                            Q: What does it do?
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                            • M mpergand

                              @Pantoufle
                              What is the format of the original data ?
                              ASCII in hex format ?
                              Binary in big endian ?
                              Other ?

                              P Offline
                              P Offline
                              Pantoufle
                              wrote on last edited by
                              #16

                              @mpergand said in Converting a QByteArray in Hexa format into an Int:

                              @Pantoufle
                              What is the format of the original data ?
                              ASCII in hex format ?
                              Binary in big endian ?
                              Other ?

                              Binary in big endian

                              @J-Hilk It works but same problem as before, the QByteArray generated by the line (auto mydata = QString("00004A9E").toLatin1();) is 8 bytes long.

                              Christian EhrlicherC jsulmJ 2 Replies Last reply
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                              • P Pantoufle

                                @mpergand said in Converting a QByteArray in Hexa format into an Int:

                                @Pantoufle
                                What is the format of the original data ?
                                ASCII in hex format ?
                                Binary in big endian ?
                                Other ?

                                Binary in big endian

                                @J-Hilk It works but same problem as before, the QByteArray generated by the line (auto mydata = QString("00004A9E").toLatin1();) is 8 bytes long.

                                Christian EhrlicherC Offline
                                Christian EhrlicherC Offline
                                Christian Ehrlicher
                                Lifetime Qt Champion
                                wrote on last edited by
                                #17

                                @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

                                the QByteArray generated by the line (auto mydata = QString("00004A9E").toLatin1();) is 8 bytes long.

                                But that's correct - you pass 8 bytes to a QString ctor and convert it back to a QByteArray.

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                                P 1 Reply Last reply
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                                • P Pantoufle

                                  @mpergand said in Converting a QByteArray in Hexa format into an Int:

                                  @Pantoufle
                                  What is the format of the original data ?
                                  ASCII in hex format ?
                                  Binary in big endian ?
                                  Other ?

                                  Binary in big endian

                                  @J-Hilk It works but same problem as before, the QByteArray generated by the line (auto mydata = QString("00004A9E").toLatin1();) is 8 bytes long.

                                  jsulmJ Offline
                                  jsulmJ Offline
                                  jsulm
                                  Lifetime Qt Champion
                                  wrote on last edited by
                                  #18

                                  @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

                                  Binary in big endian

                                  Then why do you pass a string to QByteArray?
                                  You should rather use https://doc.qt.io/qt-6/qbytearray.html#fromRawData
                                  Also see https://doc.qt.io/qt-6/qtendian.html

                                  https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                  • Christian EhrlicherC Christian Ehrlicher

                                    @Pantoufle said in Converting a QByteArray in Hexa format into an Int:

                                    the QByteArray generated by the line (auto mydata = QString("00004A9E").toLatin1();) is 8 bytes long.

                                    But that's correct - you pass 8 bytes to a QString ctor and convert it back to a QByteArray.

                                    P Offline
                                    P Offline
                                    Pantoufle
                                    wrote on last edited by
                                    #19

                                    @Christian-Ehrlicher

                                    My case is equivalent to :

                                    QByteArray mydata = QByteArray::fromHex("0000049E");

                                    Which generate a 4 bytes array, so yeah it's normal that it generates a 8 bytes in the previous example but just it's not what I want.

                                    @jsulm

                                    QByteArray mydata = QByteArray::fromHex("0000049E");
                                    Represent a binary in big endian, 4 bytes long.
                                    I didn't know about QtEndian and fromRawData, I will check that thx.
                                    Also I found that it works with QByteArrayLiteral("\x00\x00\x04\x9E")

                                    JonBJ 1 Reply Last reply
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                                    • P Pantoufle

                                      @Christian-Ehrlicher

                                      My case is equivalent to :

                                      QByteArray mydata = QByteArray::fromHex("0000049E");

                                      Which generate a 4 bytes array, so yeah it's normal that it generates a 8 bytes in the previous example but just it's not what I want.

                                      @jsulm

                                      QByteArray mydata = QByteArray::fromHex("0000049E");
                                      Represent a binary in big endian, 4 bytes long.
                                      I didn't know about QtEndian and fromRawData, I will check that thx.
                                      Also I found that it works with QByteArrayLiteral("\x00\x00\x04\x9E")

                                      JonBJ Offline
                                      JonBJ Offline
                                      JonB
                                      wrote on last edited by JonB
                                      #20

                                      @Pantoufle
                                      Hi. I don't understand if you still have a problem or a question? You want a 4 byte integer, and you have one. I don't understand what the relevance is of a string you choose to pass to QByteArray::fromHex() as a convenient way of getting the 4 bytes into memory, who cares what the string is or how long it is? It has nothing to do with how your device works, which does not use hex or strings, it just sends a 4-byte integer. Which should be convertible via QByteArray::toInt() provided the byte order matches your machine's endian order (else it would need swapping).

                                      My bad, see @Christian-Ehrlicher's clarification of QByteArray::toInt() below!

                                      Christian EhrlicherC 1 Reply Last reply
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                                      • JonBJ JonB

                                        @Pantoufle
                                        Hi. I don't understand if you still have a problem or a question? You want a 4 byte integer, and you have one. I don't understand what the relevance is of a string you choose to pass to QByteArray::fromHex() as a convenient way of getting the 4 bytes into memory, who cares what the string is or how long it is? It has nothing to do with how your device works, which does not use hex or strings, it just sends a 4-byte integer. Which should be convertible via QByteArray::toInt() provided the byte order matches your machine's endian order (else it would need swapping).

                                        My bad, see @Christian-Ehrlicher's clarification of QByteArray::toInt() below!

                                        Christian EhrlicherC Offline
                                        Christian EhrlicherC Offline
                                        Christian Ehrlicher
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #21

                                        @JonB said in Converting a QByteArray in Hexa format into an Int:

                                        Which should be convertible via QByteArray::toInt() provided the byte order matches your machine's endian order (else it would need swapping).

                                        No, you're wrong here.
                                        QByteArray::toInt() converts a string representation of a number to an integer.

                                        int32_t val = *(reinterpret_cast<int32_t*>(ba.constData()))
                                        

                                        if the endian is the same on the source and destination, otherwise use the qEndian helper functions.

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                                        JonBJ Paul ColbyP 2 Replies Last reply
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                                        • Christian EhrlicherC Christian Ehrlicher

                                          @JonB said in Converting a QByteArray in Hexa format into an Int:

                                          Which should be convertible via QByteArray::toInt() provided the byte order matches your machine's endian order (else it would need swapping).

                                          No, you're wrong here.
                                          QByteArray::toInt() converts a string representation of a number to an integer.

                                          int32_t val = *(reinterpret_cast<int32_t*>(ba.constData()))
                                          

                                          if the endian is the same on the source and destination, otherwise use the qEndian helper functions.

                                          JonBJ Offline
                                          JonBJ Offline
                                          JonB
                                          wrote on last edited by
                                          #22

                                          @Christian-Ehrlicher
                                          Oh, I am so wrong, I should have looked at QByteArray::toInt() docs before answering instead of assuming it was a binary operation! I now understand where the confusion lies totally! I will cross out my earlier.

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