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    Call for Presentations - Qt World Summit

    Unsolved How to use QFile, QByteArray and QString?

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    • V
      victor wang last edited by A Former User

      Hi, i'm using Qt5.5 in my computer.
      I'm programming a code that can read what i write in the EEprom.
      I just wanna read the valid ASCII out instead of all of the value in EEprom.
      This is my code.

      I had try to use not only readLine()、Read() but also readAll().
      But none of it do what i want.
      This is the picture that i cat from my eeprom here.

      I just want to read the word "o" in the beginning and "6" in the end.
      What can i so ?
      Please help!

      jsulm 1 Reply Last reply Reply Quote 0
      • jsulm
        jsulm Lifetime Qt Champion @victor wang last edited by

        @victor-wang What exactly does not work?
        It is just a file - so just read and parse it as any other file.

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

        V 1 Reply Last reply Reply Quote 0
        • V
          victor wang @jsulm last edited by victor wang

          @jsulm
          When i read it out it will read not only words but also the unknown symbol below the end of the word "6".

          Like this picture shows what it shows.

          how can i get avoid from the unknown words at the end?

          jsulm 1 Reply Last reply Reply Quote 0
          • jsulm
            jsulm Lifetime Qt Champion @victor wang last edited by

            @victor-wang It depends on what exactly you want to get from the file. You can read line by line until you get what you want and then stop.

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

            V 1 Reply Last reply Reply Quote 0
            • V
              victor wang @jsulm last edited by

              @jsulm
              I've used readLine() but there are some quest.
              1.How can i know it is the end of the word?
              2.Will it know by itself?

              jsulm 1 Reply Last reply Reply Quote 0
              • jsulm
                jsulm Lifetime Qt Champion @victor wang last edited by

                @victor-wang What does "word" mean? It will not know by itself, you should know.
                Can you explain EXACTLY what you want to read from the file? It is really unclear.

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

                V 1 Reply Last reply Reply Quote 0
                • V
                  victor wang @jsulm last edited by victor wang

                  @jsulm
                  I just wanna read this.
                  Not the black question marks.

                  jsulm 1 Reply Last reply Reply Quote 0
                  • jsulm
                    jsulm Lifetime Qt Champion @victor wang last edited by

                    @victor-wang And what is the problem? Just read line by line the first 6 lines.

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

                    V 1 Reply Last reply Reply Quote 0
                    • V
                      victor wang @jsulm last edited by victor wang

                      @jsulm
                      That because if there is other person who want to write things into eeprom.
                      I will show what he write in the eeprom.
                      According to this addition, I can't just read for six lines.
                      Because not every one will just write 6 lines.

                      I have to know where is the last word.

                      jsulm 1 Reply Last reply Reply Quote 0
                      • jsulm
                        jsulm Lifetime Qt Champion @victor wang last edited by

                        @victor-wang Again: what is "last word"? How is it defined? I still don't understand what information you want to get. Are those MAC2, Model, PN, ...?

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

                        V 1 Reply Last reply Reply Quote 0
                        • V
                          victor wang @jsulm last edited by victor wang

                          @jsulm

                          For example the picture i gave you.
                          The last word means the last line of the "6".
                          Picture here

                          Those words is what i write in eeprom.
                          For other example if i write "skdjb,smdnv6546321" into eeprom.
                          Then the last Alphabet is "1" and i just want to read what i write.

                          jsulm 1 Reply Last reply Reply Quote 0
                          • jsulm
                            jsulm Lifetime Qt Champion @victor wang last edited by

                            @victor-wang Then read line by line and parse each line to check whether it is what you want.
                            And you should use correct wording, else it's hard to understand what you mean: a word is not a line.

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

                            V 1 Reply Last reply Reply Quote 0
                            • V
                              victor wang @jsulm last edited by

                              @jsulm
                              Sorry, how to parse it?
                              I will not know what will other people write, how can parse?

                              jsulm 1 Reply Last reply Reply Quote 0
                              • jsulm
                                jsulm Lifetime Qt Champion @victor wang last edited by

                                @victor-wang OK, you don't know what others are writing, right? But you know what you want to read, right?
                                If so then:

                                QByteArray whatIWantToRead = "ABCD";
                                QString line = file.readLine();
                                if (line == whatIWantToRead)
                                    // do something
                                

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

                                V 1 Reply Last reply Reply Quote 1
                                • V
                                  victor wang @jsulm last edited by

                                  @jsulm
                                  If i want to read a~z、A~Z and some other exclamation mark and question mark and etc..
                                  I have to write all of it into whatIWantToRead ?

                                  jsulm 1 Reply Last reply Reply Quote 0
                                  • jsulm
                                    jsulm Lifetime Qt Champion @victor wang last edited by

                                    @victor-wang You can use regular expressions, see https://en.wikipedia.org/wiki/Regular_expression and http://doc.qt.io/qt-5.8/qregularexpression.html

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

                                    V 1 Reply Last reply Reply Quote 0
                                    • V
                                      victor wang @jsulm last edited by

                                      @jsulm
                                      Do you have an example?
                                      Or can i parse it by ASCII ?

                                      jsulm J.Hilk 2 Replies Last reply Reply Quote 0
                                      • jsulm
                                        jsulm Lifetime Qt Champion @victor wang last edited by

                                        @victor-wang There are a lot of examples for regular expressions on the Internet

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

                                        1 Reply Last reply Reply Quote 0
                                        • J.Hilk
                                          J.Hilk Moderators @victor wang last edited by

                                          @victor-wang

                                          If you know, that valid lines always contain legit chars between 'A' and 'z'

                                          You can make a simple If-statement with the first char in your bytearray:

                                          QByteArray bArray = file.readline();
                                          if(bArray[0] < QLatin1Char('A') || bArray[0] > QLatin1Char('z'))
                                               //Abort condition met
                                          

                                          use QLatin1Char if its ASCII, QChar if its unicode.

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

                                          Qt Needs YOUR vote: https://bugreports.qt.io/browse/QTQAINFRA-4121


                                          Q: What's that?
                                          A: It's blue light.
                                          Q: What does it do?
                                          A: It turns blue.

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