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  4. [SOLVED] Suggest a faster way for replacing custom parameters in a string
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[SOLVED] Suggest a faster way for replacing custom parameters in a string

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  • Chris KawaC Offline
    Chris KawaC Offline
    Chris Kawa
    Lifetime Qt Champion
    wrote on last edited by
    #6

    I'd say sum up the total length of the parameters and call reserve on the string before doing the replacements.

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    • T3STYT Offline
      T3STYT Offline
      T3STY
      wrote on last edited by
      #7

      That's a good idea! Thanks :)
      But it will still not solve the number replacements I should make... I have to think about some other strategy...

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      • T3STYT T3STY

        That's a good idea! Thanks :)
        But it will still not solve the number replacements I should make... I have to think about some other strategy...

        O Offline
        O Offline
        onek24
        wrote on last edited by
        #8

        @T3STY

        I can't provide any idea or solution, but maybe i can give you a hint - something i would try: Check out the source-code of the QString class and see what ::args(...) does. Maybe you can use Qt's code and implement the functionality to have different kinds of parameter-types(%s, %EE, ...).

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        • T3STYT Offline
          T3STYT Offline
          T3STY
          wrote on last edited by
          #9

          Unfortunately, modifying Qt's source is not a viable option because of the license I'm using (LGPL). But I think I found some strategy to maintain some const-ness in the initial string length. I am using pre-formatted strings with "<FONT class="something">%1</FONT>" html tags, so most formatting is done with CSS ( QPlainTextEdit::document::setDefaultStyleSheet() ). This will reduce the number of reallocations (before replacement) to 1 (the %1 argument) with QString::arg(), and then I replace all data in the final string. I'm also thinking about other possible tricks like asking the time to QTime::getCurrentTime() with a separate string, so I would only replace time once instead of for each parameter.

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          • Chris KawaC Offline
            Chris KawaC Offline
            Chris Kawa
            Lifetime Qt Champion
            wrote on last edited by Chris Kawa
            #10

            But it will still not solve the number replacements I should make

            You'll need to convert the numbers to strings anyway, so you can do that first and get the length of these strings.
            The problem here is that numeric conversions in Qt like Qstring::number return a new string (thus allocate memory).
            You could allocate a handful of QStrings once, reserve some space in them and then use QTextStream to make the conversions "in place".

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            • T3STYT Offline
              T3STYT Offline
              T3STY
              wrote on last edited by
              #11

              @Chris-Kawa The number to string conversion is done via QVariant::toString() anyway, so that is not a problem. And reserving space is not necessary anymore if I use the tricks above :)

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              • T3STYT T3STY

                Unfortunately, modifying Qt's source is not a viable option because of the license I'm using (LGPL). But I think I found some strategy to maintain some const-ness in the initial string length. I am using pre-formatted strings with "<FONT class="something">%1</FONT>" html tags, so most formatting is done with CSS ( QPlainTextEdit::document::setDefaultStyleSheet() ). This will reduce the number of reallocations (before replacement) to 1 (the %1 argument) with QString::arg(), and then I replace all data in the final string. I'm also thinking about other possible tricks like asking the time to QTime::getCurrentTime() with a separate string, so I would only replace time once instead of for each parameter.

                O Offline
                O Offline
                onek24
                wrote on last edited by onek24
                #12

                @T3STY said:

                Unfortunately, modifying Qt's source is not a viable option because of the license I'm using (LGPL).

                No need to modify Qt's source. Just check what Qt does in such a case and develop your own algorithm/method.

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                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #13

                  What about just doing a good old

                  QString message = "{" QTime::currentTime().toString() + el_msg[] etc.
                  

                  ?

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

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                  • T3STYT Offline
                    T3STYT Offline
                    T3STY
                    wrote on last edited by
                    #14

                    @SGaist that would make it hard to follow a pre-format string. Yes, it would be faster and, to some extent, easier. But definitely not the solution in my case.

                    Anyway, eventually I went for the HTML pre-formatted strings method that I wrote about in an earlier post. It's the easier and faster solution for me and seems to have the lightest impact on performance of all methods I have tried.

                    Thank you all for help :)

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #15

                      If you want to be sure about the performance: QBENCHMARK ;)

                      Happy coding !

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

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