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Getting values from a Huge String format= ("value : number")

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  • K kamhagh

    @p3c0 Thanks for your answer
    The problem is sometimes the GPU name might be Long or the user might have More than 1 graphics card. I don't think its a reliable solution!

    is there anyway i can take out the line as a separate String if i know the first word index? indexOf can find the "GPU Load :"

    p3c0P Offline
    p3c0P Offline
    p3c0
    Moderators
    wrote on last edited by
    #4

    @kamhagh Well then find the line which will have the string "GPU Load" using contains.

    157

    K 1 Reply Last reply
    1
    • p3c0P p3c0

      @kamhagh Well then find the line which will have the string "GPU Load" using contains.

      K Offline
      K Offline
      kamhagh
      wrote on last edited by
      #5

      @p3c0 thanks!
      but how can i take out that line using indexOf?(contains only returns true or false)

      p3c0P 1 Reply Last reply
      0
      • K kamhagh

        @p3c0 thanks!
        but how can i take out that line using indexOf?(contains only returns true or false)

        p3c0P Offline
        p3c0P Offline
        p3c0
        Moderators
        wrote on last edited by
        #6

        @kamhagh If that string is new line separated ("\n"), as it seems, split it into different strings, iterate and then check in it using contains

        QStringList list = outstr.split("\n");
        foreach(QString str, list) {
            if(str.contains("GPU load"))
                qDebug() << str.section(":",-1);
        }
        

        157

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        1
        • Chris KawaC Offline
          Chris KawaC Offline
          Chris Kawa
          Lifetime Qt Champion
          wrote on last edited by
          #7

          Split and a loop can be a slow operation if the searched string is long. It also creates a lot of copies.
          On a large inputs a faster, more memory friendly and a little more permissive of the format solution would be to use a regexp, e.g.:

          auto options = QRegularExpression::CaseInsensitiveOption;
          auto m = QRegularExpression(".*GPU load[\\s:]+([\\d.]+)%", options).match(text);
          if(m.hasMatch()) {
              float value = m.capturedRef(m.lastCapturedIndex()).toFloat();
              // do something with value
          }
          

          This allows varying amount of whitespace between the "GPU load" and the actual number and will tolerate a number in any "C" locale form e.g. 7%, 42%, 100%, 4.54534345% etc.
          Note that QStringref::toFloat will work only for "C" locale i.e XXX.XXX% format.
          If you expect anything else, e.g. comma instead of dot or thousand separators you should use QLocale::toFloat instead and modify the regexp accordingly.

          K 1 Reply Last reply
          1
          • Chris KawaC Chris Kawa

            Split and a loop can be a slow operation if the searched string is long. It also creates a lot of copies.
            On a large inputs a faster, more memory friendly and a little more permissive of the format solution would be to use a regexp, e.g.:

            auto options = QRegularExpression::CaseInsensitiveOption;
            auto m = QRegularExpression(".*GPU load[\\s:]+([\\d.]+)%", options).match(text);
            if(m.hasMatch()) {
                float value = m.capturedRef(m.lastCapturedIndex()).toFloat();
                // do something with value
            }
            

            This allows varying amount of whitespace between the "GPU load" and the actual number and will tolerate a number in any "C" locale form e.g. 7%, 42%, 100%, 4.54534345% etc.
            Note that QStringref::toFloat will work only for "C" locale i.e XXX.XXX% format.
            If you expect anything else, e.g. comma instead of dot or thousand separators you should use QLocale::toFloat instead and modify the regexp accordingly.

            K Offline
            K Offline
            kamhagh
            wrote on last edited by
            #8

            @Chris-Kawa thanks! that looks wierd, and like alien language to me but i'm googling about regexp! and than i guess i'll figure it out :D

            Chris KawaC 1 Reply Last reply
            0
            • K kamhagh

              @Chris-Kawa thanks! that looks wierd, and like alien language to me but i'm googling about regexp! and than i guess i'll figure it out :D

              Chris KawaC Offline
              Chris KawaC Offline
              Chris Kawa
              Lifetime Qt Champion
              wrote on last edited by
              #9

              @kamhagh said:

              thanks! that looks wierd, and like alien language to me

              haha. To you and me both ;) Regexps should not be the first thing to go to in most cases but they are powerful and should land in every programmer's toolbox at some point. They are great at parsing blocks of text and flexibly extracting pieces of it.

              Basically in this case the interesting part of the regexp is the ([\\d.]+) part. The () is a capture group. Anything matched in that will be placed in an array of results accessed by capturedRef(). The []+ part says "anything inside the brackets at least once". \\d means "any digit" and . is, well, a dot character.
              Other stuff: .* means "any character 0 or more times", [\\s:]+ means "at least one whitespace or :".
              The \\ are unfortunate result of c++ standard. The actual characters needed by regexp are just \, but since it's in a c++ string literal we need to escape it and thus it becomes \\.

              K 1 Reply Last reply
              1
              • Chris KawaC Chris Kawa

                @kamhagh said:

                thanks! that looks wierd, and like alien language to me

                haha. To you and me both ;) Regexps should not be the first thing to go to in most cases but they are powerful and should land in every programmer's toolbox at some point. They are great at parsing blocks of text and flexibly extracting pieces of it.

                Basically in this case the interesting part of the regexp is the ([\\d.]+) part. The () is a capture group. Anything matched in that will be placed in an array of results accessed by capturedRef(). The []+ part says "anything inside the brackets at least once". \\d means "any digit" and . is, well, a dot character.
                Other stuff: .* means "any character 0 or more times", [\\s:]+ means "at least one whitespace or :".
                The \\ are unfortunate result of c++ standard. The actual characters needed by regexp are just \, but since it's in a c++ string literal we need to escape it and thus it becomes \\.

                K Offline
                K Offline
                kamhagh
                wrote on last edited by kamhagh
                #10

                @Chris-Kawa
                thanks! now I understand!

                But I get this while trying to compile:

                **C:\Qt\Qt5.3.0\Tools\QtCreator\bin\regexTemp\main.cpp:14: error: 'options' does not name a type
                auto options = QRegularExpression::CaseInsensitiveOption;
                ^

                C:\Qt\Qt5.3.0\Tools\QtCreator\bin\regexTemp\main.cpp:15: error: 'm' does not name a type
                auto m = QRegularExpression(".*GPU load[\s:]+([\d.]+)%", options).match(outstr);
                ^

                C:\Qt\Qt5.3.0\Tools\QtCreator\bin\regexTemp\main.cpp:16: error: 'm' was not declared in this scope
                if(m.hasMatch()) {
                ^
                ^**

                after i add c++11 option to .pro file i get these

                C:\Qt\Qt5.3.0\Tools\QtCreator\bin\regexTemp\main.cpp:14: error: incomplete type 'QRegularExpression' used in nested name specifier
                auto options = QRegularExpression::CaseInsensitiveOption;
                ^

                C:\Qt\Qt5.3.0\Tools\QtCreator\bin\regexTemp\main.cpp:15: error: invalid use of incomplete type 'class QRegularExpression'
                auto m = QRegularExpression(".*GPU load[\s:]+([\d.]+)%", options).match(outstr);
                ^
                C:\Qt\Qt5.3.0\5.3\mingw482_32\include\QtCore\qstring.h:78: error: forward declaration of 'class QRegularExpression'
                class QRegularExpression;
                ^

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                0
                • Chris KawaC Offline
                  Chris KawaC Offline
                  Chris Kawa
                  Lifetime Qt Champion
                  wrote on last edited by
                  #11

                  You are missing an include: #include <QRegularExpression>.

                  K 1 Reply Last reply
                  1
                  • Chris KawaC Chris Kawa

                    You are missing an include: #include <QRegularExpression>.

                    K Offline
                    K Offline
                    kamhagh
                    wrote on last edited by kamhagh
                    #12

                    @Chris-Kawa
                    oh..... im going to kill myself :| how could I forget about that:D sorry!

                    thanks a lot!

                    but one last question, Do stuff like Program save files(quake arena if you've ever played it, or warcraft, basically old games or metro!) or Raspberry pi's setting(these are all i can think of + MSI Afterburner) use regexps to read save files?

                    1 Reply Last reply
                    0
                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #13

                      Hi,

                      If you want to toy around with QRegularExpression, a new version of the regexp tool can be found in examples/widgets/tools/regularexpression. It might be available only in the dev branch currently but you can build it with any Qt version including QRegularExpression.

                      Hope it helps

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                      1 Reply Last reply
                      1
                      • Chris KawaC Offline
                        Chris KawaC Offline
                        Chris Kawa
                        Lifetime Qt Champion
                        wrote on last edited by
                        #14

                        There's no way to say how these programs parse their files without looking at their source but I doubt they use regexps for that.

                        Regexps are best when the content you want to parse is fuzzy e.g. it can be uppercase, lowercase, spaces or tabs, comma or dot, unknown or partially known data patterns etc.
                        A user input of some sort or a spill from some diagnostic tool are good examples, where you want to just grab a piece of data you know the format of and don't care about its surrounding.

                        If you design your own app and thus define the format of your files you know what is where and you can assume stuff to make the parsing faster e.g "ABC tag always comes after XYZ tag so don't bother to check for it before".
                        In that case an incremental or structured parser can be a better and a lot faster solution. Regexp are flexible but come at a cost. They're sort of a heavy artillery of parsers.
                        An example of structural parser is QSettings used with QSettings::IniFormat to parse .ini files or a QDomDocument to parse an xml.
                        An example of incremental parser is a QXmlStreamReader that provides way to read an xml file "a token at a time" and decide what to do with it.

                        K 1 Reply Last reply
                        0
                        • Chris KawaC Chris Kawa

                          There's no way to say how these programs parse their files without looking at their source but I doubt they use regexps for that.

                          Regexps are best when the content you want to parse is fuzzy e.g. it can be uppercase, lowercase, spaces or tabs, comma or dot, unknown or partially known data patterns etc.
                          A user input of some sort or a spill from some diagnostic tool are good examples, where you want to just grab a piece of data you know the format of and don't care about its surrounding.

                          If you design your own app and thus define the format of your files you know what is where and you can assume stuff to make the parsing faster e.g "ABC tag always comes after XYZ tag so don't bother to check for it before".
                          In that case an incremental or structured parser can be a better and a lot faster solution. Regexp are flexible but come at a cost. They're sort of a heavy artillery of parsers.
                          An example of structural parser is QSettings used with QSettings::IniFormat to parse .ini files or a QDomDocument to parse an xml.
                          An example of incremental parser is a QXmlStreamReader that provides way to read an xml file "a token at a time" and decide what to do with it.

                          K Offline
                          K Offline
                          kamhagh
                          wrote on last edited by
                          #15

                          @Chris-Kawa
                          oh thanks, I just thought it's always faster than doing that!

                          and thanks @SGaist i will take a look at that!

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