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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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  • SGaistS Offline
    SGaistS Offline
    SGaist
    Lifetime Qt Champion
    wrote on last edited by
    #2

    Hi,

    Can you show an example of string that your are building ?

    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 T3STY
      #3

      The string could be anything, really. It could include any number of parameters and other text. This is one:

      "[%HH:%mm:%s.%zzz] operation completed (%EE) %M"
      

      And that's the code I'm using at the moment:

      void consoleWidget::print(QVariant message, errorLevel EL){
          // using a QVariant to allow printing both strings and numeric data types 
          // get current local time
          QTime curTime(QTime::currentTime());
          
          // error level messages; el_msg[0] must not be empty (using a space) to prevent QString::at() crashing the application ->
          const QString el_msg[4] = {" ", "info", "warning", "error"};
          
          // replace parameters with data with the format specified in _format
          // _format is a private (pointer to) QString storing the message format to print, such as:
          // "[%HH:%mm:%s.%zzz] operation completed (%EE) %M"
          QString tmpMsg(*_format);
          // hour, leading zero, 00-23 or 01-12AM/PM
          tmpMsg.replace("%hh", curTime.toString("hh"));
          // hour, 0-23 or 1-12AM/PM
          tmpMsg.replace("%h",  curTime.toString("h") );
          // hour, 0-23
          tmpMsg.replace("%HH", curTime.toString("HH"));
          // minutes, 0-59
          tmpMsg.replace("%H",  curTime.toString("H") );
          // minutes, leading 0, 00-59
          tmpMsg.replace("%mm", curTime.toString("mm"));
          // hour, leading 0, 00-23
          tmpMsg.replace("%m",  curTime.toString("m") );
          // seconds, leading 0, 00-59
          tmpMsg.replace("%ss", curTime.toString("ss"));
          // seconds, 0-59
          tmpMsg.replace("%s",  curTime.toString("s") );
          // milliseconds, leading 0, 000-999
          tmpMsg.replace("%zzz",curTime.toString("zzz"));
          // milliseconds, 0-999
          tmpMsg.replace("%z",  curTime.toString("z") );
          // am/pm (lowercase)
          tmpMsg.replace("%a",  curTime.toString("a") );
          // AM/PM (UPPERCASE)
          tmpMsg.replace("%A",  curTime.toString("A") );
          // timezone
          tmpMsg.replace("%t",  curTime.toString("t") );
          
          // error level, lowercase, extended:    error, warning, info, (empty)
          tmpMsg.replace("%ee",  el_msg[EL]);
          // error level, lowercase, abbreviated: e, w, i, (empty)
          tmpMsg.replace("%e" ,  el_msg[EL].at(0));
          // error level, UPPERCASE, extended:    ERROR, WARNING, INFO, (empty)
          tmpMsg.replace("%EE",  el_msg[EL].toUpper());
          // error level, UPPERCASE, abbreviated: E, W, I, (empty)
          tmpMsg.replace("%E" ,  el_msg[EL].at(0).toUpper());
          
          // replace user message parameter with data
          // Most QVariant stored types can be converted to QString, it's safe not to check for conversion availability
          tmpMsg.replace("%M", message.toString());
          
          // will be replaced with appendHtml()
          this->appendPlainText(tmpMsg);
      }
      
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      • mrjjM Offline
        mrjjM Offline
        mrjj
        Lifetime Qt Champion
        wrote on last edited by
        #4

        @T3STY said:

        "[%HH:%mm:%s.%zzz] operation completed (%EE) %M"

        If that is a typically length of your source string then something like

        tmpMsg.replace("%a", " <b>" + curTime.toString("a") + "</b>");

        Should be fast enough ?
        Or Am I completely misunderstanding the question ?

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        • T3STYT Offline
          T3STYT Offline
          T3STY
          wrote on last edited by T3STY
          #5

          That is what I was thinking to use. However, I was asking if there was anything that would replace all the parameters at once.
          Replacing strings so many times with QString::replace() causes a lot of memory reallocation in order to expand the string size to fit requirements, which also causes more CPU usage. While increasing the string size to twice every allocation is fast enough, doing so 3 or 4 times for 30 strings causes a huge performance loss.
          So, if there was any way to tell QString::replace() (or some other method) about more things to replace at once I think it would definitely be faster and cheaper for the memory.

          BTW, The format string could be made of even 20 parameters with extra (non parametric) words. Consider:

          "h: %h | hh: %hh | H: %h | HH: %HH | m: %m | mm: %mm | s: %s | ss: %ss | z: %z | zzz: %zzz | a: %a | A: %A |  | t: %t | e: %e | E: %E | ee: %ee | EE: %EE |  | %M"
          

          which includes only part of the parameters I want to implement. Also %M is a user message that could be even hundred of characters long. There is no typical string length that I could consider to reserve memory in advance.

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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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