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Convert QbyteArray to qreal

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  • D Offline
    D Offline
    dziko147
    wrote on last edited by
    #14

    Still not working :/ :/
    I get this value

         1.36179e+30
    
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    0
    • D Offline
      D Offline
      dziko147
      wrote on last edited by
      #15

      Currently I test a static QByteArray .
      this is my code :
      QByteArray rpmdata = "FF10001000100010001000100010001000";
      qDebug() << rpmdata << "this is data" ;

      QDataStream stream(rpmdata);

      quint8 byte;
      qreal rpmint;
      stream >> byte; // skip first byte
      stream >> rpmint; // read float value
      qDebug() << rpmint << "this is data to int" ;

      back.setValue(rpmint);
      
      KroMignonK 1 Reply Last reply
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      • D dziko147

        Currently I test a static QByteArray .
        this is my code :
        QByteArray rpmdata = "FF10001000100010001000100010001000";
        qDebug() << rpmdata << "this is data" ;

        QDataStream stream(rpmdata);

        quint8 byte;
        qreal rpmint;
        stream >> byte; // skip first byte
        stream >> rpmint; // read float value
        qDebug() << rpmint << "this is data to int" ;

        back.setValue(rpmint);
        
        KroMignonK Offline
        KroMignonK Offline
        KroMignon
        wrote on last edited by
        #16

        @dziko147 said in Convert QbyteArray to qreal:

        Currently I test a static QByteArray .
        this is my code :
        QByteArray rpmdata = "FF10001000100010001000100010001000";

        What do you want to do with this?

        If the data are hexadecimal coded, then you have to convert them to binary:

        QByteArray rpmdata = QByteArray::fromHex("FF10001000100010001000100010001000");
        

        ==> https://doc.qt.io/qt-5/qbytearray.html#fromHex

        It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

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        • D Offline
          D Offline
          dziko147
          wrote on last edited by
          #17

          @KroMignon
          So I try to receive data from QCanBusFrame .
          So I extract the payload using : QByteArray QCanBusFrame::payload() const .
          Currently I try to test a static QByteArray (I mean that i write manually the QByteArray) wich is the "rpmdata " .
          the type of my value is real .
          the frame compouned of 5byte( 1 for status and 4 for data) .
          I hope that my problem looks clear .

          KroMignonK 1 Reply Last reply
          0
          • Christian EhrlicherC Online
            Christian EhrlicherC Online
            Christian Ehrlicher
            Lifetime Qt Champion
            wrote on last edited by
            #18

            @dziko147 said in Convert QbyteArray to qreal:

            I hope that my problem looks clear .

            No since you still not tell us how the sender encodes the data and what value you expect.

            Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
            Visit the Qt Academy at https://academy.qt.io/catalog

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            • D dziko147

              @KroMignon
              So I try to receive data from QCanBusFrame .
              So I extract the payload using : QByteArray QCanBusFrame::payload() const .
              Currently I try to test a static QByteArray (I mean that i write manually the QByteArray) wich is the "rpmdata " .
              the type of my value is real .
              the frame compouned of 5byte( 1 for status and 4 for data) .
              I hope that my problem looks clear .

              KroMignonK Offline
              KroMignonK Offline
              KroMignon
              wrote on last edited by
              #19

              @dziko147 said in Convert QbyteArray to qreal:

              I hope that my problem looks clear .

              Sorry but it is not clear to me :-(

              What do represents "FF10001000100010001000100010001000", which is your test data?

              It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

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              1
              • D Offline
                D Offline
                dziko147
                wrote on last edited by
                #20

                @KroMignon Exact . I write manually this test data .
                @Christian-Ehrlicher I will receive a frame using QCanBusFrame , So the data will be in a QByteArray variable . I expect a Rpm Value wich is real .

                Christian EhrlicherC KroMignonK 2 Replies Last reply
                0
                • D dziko147

                  @KroMignon Exact . I write manually this test data .
                  @Christian-Ehrlicher I will receive a frame using QCanBusFrame , So the data will be in a QByteArray variable . I expect a Rpm Value wich is real .

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

                  @dziko147 said in Convert QbyteArray to qreal:

                  . I expect a Rpm Value wich is real .

                  This tells us nothing. real just tells that the value is a floating-point value. It does not tell how this value is encoded and since you can't/won't tell us this you have to find it out by yourself. Two possibilities were already given to you, other encodings are unknown to us and therefore you're on your own when none of them works.

                  Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                  Visit the Qt Academy at https://academy.qt.io/catalog

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                  • D dziko147

                    @KroMignon Exact . I write manually this test data .
                    @Christian-Ehrlicher I will receive a frame using QCanBusFrame , So the data will be in a QByteArray variable . I expect a Rpm Value wich is real .

                    KroMignonK Offline
                    KroMignonK Offline
                    KroMignon
                    wrote on last edited by KroMignon
                    #22

                    @dziko147 said in Convert QbyteArray to qreal:

                    Exact . I write manually this test data .

                    I don't know how to say it more clearly:

                    • What does this represent?
                    • Is it a hexadecimal representation of your test data?
                    • CAN frame have a maximum of 8 Byte of payload, this is much more data, so what is it?

                    You should be able to answer those questions, or you are not knowing what you are doing. Which is very bad.

                    It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

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                    2
                    • D Offline
                      D Offline
                      dziko147
                      wrote on last edited by
                      #23

                      @Christian-Ehrlicher I do not know how the sender encodes the data .
                      What I know is I receive data using the QCanBusFrame . then I extract the data .
                      So i get a QByteArray Data . I want to convert it .

                      JonBJ jsulmJ 2 Replies Last reply
                      0
                      • D Offline
                        D Offline
                        dziko147
                        wrote on last edited by
                        #24

                        @KroMignon Can you give me an example of a QByteArray compouned of 5bytes ?

                        KroMignonK 1 Reply Last reply
                        0
                        • D dziko147

                          @KroMignon Can you give me an example of a QByteArray compouned of 5bytes ?

                          KroMignonK Offline
                          KroMignonK Offline
                          KroMignon
                          wrote on last edited by
                          #25

                          @dziko147 said in Convert QbyteArray to qreal:

                          Can you give me an example of a QByteArray compouned of 5bytes ?

                          Yes, here are many examples:

                          QByteArray b1("ABCDE");
                          QByteArray b2;
                          b2.resize(5);
                          b2[0] = 0x3c;
                          b2[1] = 0xb8;
                          b2[2] = 0x64;
                          b2[3] = 0x18;
                          b3[4] = 0xca;
                          
                          QByteArray b3 = QByteArray:fromHex("0102030405");
                          

                          It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

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                          3
                          • D dziko147

                            @Christian-Ehrlicher I do not know how the sender encodes the data .
                            What I know is I receive data using the QCanBusFrame . then I extract the data .
                            So i get a QByteArray Data . I want to convert it .

                            JonBJ Offline
                            JonBJ Offline
                            JonB
                            wrote on last edited by
                            #26

                            @dziko147 said in Convert QbyteArray to qreal:

                            @Christian-Ehrlicher I do not know how the sender encodes the data .

                            If you do not know how the data is encoded/sent, @Christian-Ehrlicher does not....

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                            0
                            • D Offline
                              D Offline
                              dziko147
                              wrote on last edited by
                              #27

                              @KroMignon
                              I get value =0 after converting :/

                              JonBJ KroMignonK 2 Replies Last reply
                              0
                              • D dziko147

                                @Christian-Ehrlicher I do not know how the sender encodes the data .
                                What I know is I receive data using the QCanBusFrame . then I extract the data .
                                So i get a QByteArray Data . I want to convert it .

                                jsulmJ Offline
                                jsulmJ Offline
                                jsulm
                                Lifetime Qt Champion
                                wrote on last edited by
                                #28

                                @dziko147 said in Convert QbyteArray to qreal:

                                I do not know how the sender encodes the data

                                Then how do you want to decode it?
                                You should at least get some data from sender where you know what exact numbers the sender sent, then you can try to find out how the data was encoded.

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

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                                0
                                • D dziko147

                                  @KroMignon
                                  I get value =0 after converting :/

                                  JonBJ Offline
                                  JonBJ Offline
                                  JonB
                                  wrote on last edited by JonB
                                  #29

                                  @dziko147
                                  After converting.... what? how?

                                  Tell you what: tell us two things:

                                  1. Forget about converting anything to float. Show us what the values of the first 5 bytes you receive are. (You say the first byte is a status byte and the next 4 bytes are the value you are interested in, right?)
                                  2. Tell us what floating point number you know that encodes/conveys/sends. (Please make sure it is not 0!)
                                  1 Reply Last reply
                                  1
                                  • D dziko147

                                    @KroMignon
                                    I get value =0 after converting :/

                                    KroMignonK Offline
                                    KroMignonK Offline
                                    KroMignon
                                    wrote on last edited by
                                    #30

                                    @dziko147 said in Convert QbyteArray to qreal:

                                    I get value =0 after converting :/

                                    After converting what?
                                    Please, take time to understand what are the data you want to convert.
                                    I cannot do this for you!

                                    It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                                    D 1 Reply Last reply
                                    1
                                    • KroMignonK KroMignon

                                      @dziko147 said in Convert QbyteArray to qreal:

                                      I get value =0 after converting :/

                                      After converting what?
                                      Please, take time to understand what are the data you want to convert.
                                      I cannot do this for you!

                                      D Offline
                                      D Offline
                                      dziko147
                                      wrote on last edited by
                                      #31

                                      @KroMignon
                                      QByteArray rpmdata = QByteArray::fromHex("0102030405"); ---> I want to
                                      convert this .
                                      qDebug() << rpmdata << "this is data" ;
                                      QDataStream stream(rpmdata);
                                      quint8 byte;
                                      float rpmfloat;
                                      stream >> byte; // skip first byte
                                      stream >> rpmfloat; // read float value
                                      qDebug() << rpmfloat << "this is data to float" ;
                                      back.setValue(rpmfloat); ----> I display the value converted here .

                                      JonBJ KroMignonK 2 Replies Last reply
                                      0
                                      • D dziko147

                                        @KroMignon
                                        QByteArray rpmdata = QByteArray::fromHex("0102030405"); ---> I want to
                                        convert this .
                                        qDebug() << rpmdata << "this is data" ;
                                        QDataStream stream(rpmdata);
                                        quint8 byte;
                                        float rpmfloat;
                                        stream >> byte; // skip first byte
                                        stream >> rpmfloat; // read float value
                                        qDebug() << rpmfloat << "this is data to float" ;
                                        back.setValue(rpmfloat); ----> I display the value converted here .

                                        JonBJ Offline
                                        JonBJ Offline
                                        JonB
                                        wrote on last edited by JonB
                                        #32

                                        @dziko147
                                        You push raw bytes into a QDataStream. You then try to read that back as, say, a float.

                                        Unless I have misunderstood QDataStream you cannot do that. It is a structured stream. E.g. it will (well, should) contain "markers" for the data and its types.

                                        Experts, I am right here, aren't I (have never used QDataStream)?

                                        UPDATE
                                        For anyone reading this, the expert answers below indicate this is not the case, and my understanding was incorrect.

                                        Christian EhrlicherC KroMignonK 2 Replies Last reply
                                        0
                                        • JonBJ JonB

                                          @dziko147
                                          You push raw bytes into a QDataStream. You then try to read that back as, say, a float.

                                          Unless I have misunderstood QDataStream you cannot do that. It is a structured stream. E.g. it will (well, should) contain "markers" for the data and its types.

                                          Experts, I am right here, aren't I (have never used QDataStream)?

                                          UPDATE
                                          For anyone reading this, the expert answers below indicate this is not the case, and my understanding was incorrect.

                                          Christian EhrlicherC Online
                                          Christian EhrlicherC Online
                                          Christian Ehrlicher
                                          Lifetime Qt Champion
                                          wrote on last edited by
                                          #33

                                          @JonB said in Convert QbyteArray to qreal:

                                          E.g. it will (well, should) contain "markers" for the data and its types.

                                          Not for PODs. For QString e.g. a length field is added. What is added for which build-in Qt type is not documented - QDataStream is not meant to be used with anything else than a QDataStream.

                                          Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                                          Visit the Qt Academy at https://academy.qt.io/catalog

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