Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. General talk
  3. The Lounge
  4. Recurring C++ and Qt anti-patterns
Forum Updated to NodeBB v4.3 + New Features

Recurring C++ and Qt anti-patterns

Scheduled Pinned Locked Moved The Lounge
126 Posts 17 Posters 71.1k Views 10 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • JonBJ JonB

    @jsulm
    No, the whole point is that the "Pythonic" way is precisely to go try ... except instead of checking via in, that's my point! Same with division by 0, and other cases. This is Python's "Ask for forgiveness, not for permission" philosophy. Note that personally I wrote

    Am I good Python citizen? Am I, heck no! If nothing else, it gets in the way of having the choice to break on any exception in a debugger.

    :)

    kshegunovK Offline
    kshegunovK Offline
    kshegunov
    Moderators
    wrote on last edited by kshegunov
    #93

    @JonB said in Recurring C++ and Qt anti-patterns:

    Same with division by 0, and other cases.

    Out of curiosity: How does python handle that, because as far as I know (I don't really know that much, but bear with me for a second) there's no (strong) typing and while dividing by int(0) is invalid, division by double(0) is valid?

    Read and abide by the Qt Code of Conduct

    JonBJ 1 Reply Last reply
    0
    • kshegunovK kshegunov

      @JonB said in Recurring C++ and Qt anti-patterns:

      Same with division by 0, and other cases.

      Out of curiosity: How does python handle that, because as far as I know (I don't really know that much, but bear with me for a second) there's no (strong) typing and while dividing by int(0) is invalid, division by double(0) is valid?

      JonBJ Online
      JonBJ Online
      JonB
      wrote on last edited by
      #94

      @kshegunov
      I am just reporting that the "Pythonic" way to do division, where the divisor might be zero, is to do the divide unconditionally and catch the exception. As soon as I see "Pythonic" I tend to ignore it, and do what I'd do in C++ instead, but that's just me :)

      What I can show you is the following output:

      >>> z = 1 / 0
      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
      ZeroDivisionError: division by zero
      >>> z = 1.5 / 0.0
      Traceback (most recent call last):
        File "<stdin>", line 1, in <module>
      ZeroDivisionError: float division by zero
      >>> 
      

      So you get a ZeroDivisionError either way (which you could catch in a try ... except ZeroDivisionError), though by the look of it the error message distinguishes between plain division by zero versus float division by zero :)

      kshegunovK 1 Reply Last reply
      1
      • JonBJ JonB

        @kshegunov
        I am just reporting that the "Pythonic" way to do division, where the divisor might be zero, is to do the divide unconditionally and catch the exception. As soon as I see "Pythonic" I tend to ignore it, and do what I'd do in C++ instead, but that's just me :)

        What I can show you is the following output:

        >>> z = 1 / 0
        Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
        ZeroDivisionError: division by zero
        >>> z = 1.5 / 0.0
        Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
        ZeroDivisionError: float division by zero
        >>> 
        

        So you get a ZeroDivisionError either way (which you could catch in a try ... except ZeroDivisionError), though by the look of it the error message distinguishes between plain division by zero versus float division by zero :)

        kshegunovK Offline
        kshegunovK Offline
        kshegunov
        Moderators
        wrote on last edited by
        #95

        @JonB said in Recurring C++ and Qt anti-patterns:

        As soon as I see "Pythonic" I tend to ignore it, and do what I'd do in C++ instead, but that's just me

        You're a wise man ... ;)

        What I can show you is the following output

        Thanks, curiosity satisfied. So python just raises an exception even if dividing by a double(0) is a valid operation. Fair enough.

        Read and abide by the Qt Code of Conduct

        JonBJ 1 Reply Last reply
        0
        • kshegunovK kshegunov

          @JonB said in Recurring C++ and Qt anti-patterns:

          As soon as I see "Pythonic" I tend to ignore it, and do what I'd do in C++ instead, but that's just me

          You're a wise man ... ;)

          What I can show you is the following output

          Thanks, curiosity satisfied. So python just raises an exception even if dividing by a double(0) is a valid operation. Fair enough.

          JonBJ Online
          JonBJ Online
          JonB
          wrote on last edited by JonB
          #96

          @kshegunov
          I don't want to get into a debate (I know what you're like :) ), and I do know about floating point numbers being approximate representations (though zero/0.0 does have an exact representation), but (IMHO!) it is only in your physics/quantum mechanics area that "dividing by a double(0) is a valid operation" (the area where you can magic-away infinities and so on!). In a program it is not. (What have I let myself in for...!)

          kshegunovK 1 Reply Last reply
          0
          • JonBJ JonB

            @kshegunov
            I don't want to get into a debate (I know what you're like :) ), and I do know about floating point numbers being approximate representations (though zero/0.0 does have an exact representation), but (IMHO!) it is only in your physics/quantum mechanics area that "dividing by a double(0) is a valid operation" (the area where you can magic-away infinities and so on!). In a program it is not. (What have I let myself in for...!)

            kshegunovK Offline
            kshegunovK Offline
            kshegunov
            Moderators
            wrote on last edited by
            #97

            @JonB said in Recurring C++ and Qt anti-patterns:

            I know what you're like

            Hey! Words can hurt, you know! ;)

            though zero/0.0 does have an exact representation

            Yes, actually two representations, as with the actual zero. You have +0.0 and -0.0.

            it is only in your physics/quantum mechanics area that "dividing by a double(0) is a valid operation"

            Eh, I didn't write the IEEE standard. Take your beef with prof. Kahan.

            In a program it is not

            Actually if you look through the math.h implementations you're going to see a lot of handling for such cases. For example the people who wrote them had the decency to actually handle these special cases like log(0) returning -inf. While I agree it's not often useful to divide by zero it sometimes can be, so that's the reason to handle it like that, I assume.

            Read and abide by the Qt Code of Conduct

            JonBJ 1 Reply Last reply
            5
            • kshegunovK kshegunov

              @JonB said in Recurring C++ and Qt anti-patterns:

              I know what you're like

              Hey! Words can hurt, you know! ;)

              though zero/0.0 does have an exact representation

              Yes, actually two representations, as with the actual zero. You have +0.0 and -0.0.

              it is only in your physics/quantum mechanics area that "dividing by a double(0) is a valid operation"

              Eh, I didn't write the IEEE standard. Take your beef with prof. Kahan.

              In a program it is not

              Actually if you look through the math.h implementations you're going to see a lot of handling for such cases. For example the people who wrote them had the decency to actually handle these special cases like log(0) returning -inf. While I agree it's not often useful to divide by zero it sometimes can be, so that's the reason to handle it like that, I assume.

              JonBJ Online
              JonBJ Online
              JonB
              wrote on last edited by JonB
              #98

              @kshegunov said in Recurring C++ and Qt anti-patterns:

              You have +0.0 and -0.0

              The next time someone asks how much money I have in my pocket I will remember to give this answer.

              I have $123.45 to give away. I want to hand each person $0.00. How many people do I need to meet to get rid of all my cash? :)

              kshegunovK 1 Reply Last reply
              0
              • JonBJ JonB

                @kshegunov said in Recurring C++ and Qt anti-patterns:

                You have +0.0 and -0.0

                The next time someone asks how much money I have in my pocket I will remember to give this answer.

                I have $123.45 to give away. I want to hand each person $0.00. How many people do I need to meet to get rid of all my cash? :)

                kshegunovK Offline
                kshegunovK Offline
                kshegunov
                Moderators
                wrote on last edited by
                #99

                Here: https://en.wikipedia.org/wiki/Riemann_series_theorem
                Knock yourself out ... ;P

                Read and abide by the Qt Code of Conduct

                1 Reply Last reply
                1
                • fcarneyF Offline
                  fcarneyF Offline
                  fcarney
                  wrote on last edited by
                  #100

                  Be careful with not doing things the pythonic way in python. A lot of the time doing it the pythonic way leverages the internals of the language. In other words it pushes the execution from the interpreter to the built in methods that are written in C. So it can have an effect on performance. I don't think the exception example does this though. There may be other reasons I am not aware of.

                  C++ is a perfectly valid school of magic.

                  1 Reply Last reply
                  1
                  • Kent-DorfmanK Offline
                    Kent-DorfmanK Offline
                    Kent-Dorfman
                    wrote on last edited by
                    #101

                    wait a cotton pickin minute! there is no explicit cast to double in python so the x/double(0) argument is invalid on that basis alone...and x/float(0) behaves as expected.

                    1 Reply Last reply
                    0
                    • fcarneyF Offline
                      fcarneyF Offline
                      fcarney
                      wrote on last edited by
                      #102

                      Uncomfortable admission:
                      I wrote windows specfic code today...

                      C++ is a perfectly valid school of magic.

                      sierdzioS 1 Reply Last reply
                      3
                      • fcarneyF fcarney

                        Uncomfortable admission:
                        I wrote windows specfic code today...

                        sierdzioS Offline
                        sierdzioS Offline
                        sierdzio
                        Moderators
                        wrote on last edited by
                        #103

                        @fcarney said in Recurring C++ and Qt anti-patterns:

                        Uncomfortable admission:
                        I wrote windows specfic code today...

                        We feel for you :D

                        (Z(:^

                        1 Reply Last reply
                        2
                        • fcarneyF Offline
                          fcarneyF Offline
                          fcarney
                          wrote on last edited by
                          #104

                          Here is a nice QML anti-pattern:

                          Column {
                              Rectangle {
                                  height: parent.height
                              }
                          }
                          

                          This one was "fun". Yeah, it doesn't necessarily detect the loop and it locks up the desktop (Gnome). So you have to kill the process manually from a terminal outside of the desktop (ctrl-alt-f4).

                          C++ is a perfectly valid school of magic.

                          ODБOïO 1 Reply Last reply
                          0
                          • fcarneyF fcarney

                            Here is a nice QML anti-pattern:

                            Column {
                                Rectangle {
                                    height: parent.height
                                }
                            }
                            

                            This one was "fun". Yeah, it doesn't necessarily detect the loop and it locks up the desktop (Gnome). So you have to kill the process manually from a terminal outside of the desktop (ctrl-alt-f4).

                            ODБOïO Offline
                            ODБOïO Offline
                            ODБOï
                            wrote on last edited by
                            #105

                            @fcarney said in Recurring C++ and Qt anti-patterns:

                            Gnome

                            this code works properly on windows with Qt_5_14_0_MinGW_64_bit

                            1 Reply Last reply
                            0
                            • JonBJ Online
                              JonBJ Online
                              JonB
                              wrote on last edited by
                              #106

                              From https://forum.qt.io/topic/113223/check-whether-a-script-exists-by-script-name/14

                              QProcess process;
                              process.setStandardOutputFile(QProcess::nullDevice());
                              if (!process.startDetached(progName, args))
                              ...
                              

                              Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                              kshegunovK 1 Reply Last reply
                              0
                              • SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #107

                                AFAIK, there's nothing wrong with that. It's just that in the case you are showing, the static method has a specific behaviour that makes it unsuitable to be called like that.

                                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
                                2
                                • JonBJ JonB

                                  From https://forum.qt.io/topic/113223/check-whether-a-script-exists-by-script-name/14

                                  QProcess process;
                                  process.setStandardOutputFile(QProcess::nullDevice());
                                  if (!process.startDetached(progName, args))
                                  ...
                                  

                                  Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                                  kshegunovK Offline
                                  kshegunovK Offline
                                  kshegunov
                                  Moderators
                                  wrote on last edited by kshegunov
                                  #108

                                  @JonB said in Recurring C++ and Qt anti-patterns:

                                  Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                                  Because the class is known and that's all that matters. Whether you call it through an object or with its qualified name makes no difference. Actually, there's one widespread use of that in the Qt documentation:

                                  int main(int argc, char *argv[])
                                  {
                                      QApplication app(argc, argv);
                                      return app.exec(); // QCoreApplication::exec is static
                                  }
                                  

                                  Read and abide by the Qt Code of Conduct

                                  JonBJ 1 Reply Last reply
                                  2
                                  • kshegunovK kshegunov

                                    @JonB said in Recurring C++ and Qt anti-patterns:

                                    Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                                    Because the class is known and that's all that matters. Whether you call it through an object or with its qualified name makes no difference. Actually, there's one widespread use of that in the Qt documentation:

                                    int main(int argc, char *argv[])
                                    {
                                        QApplication app(argc, argv);
                                        return app.exec(); // QCoreApplication::exec is static
                                    }
                                    
                                    JonBJ Online
                                    JonBJ Online
                                    JonB
                                    wrote on last edited by JonB
                                    #109

                                    @kshegunov
                                    But that is not my point/question. Which is: this piece of code is not the first (or the last) where someone has mistakenly written this. If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option? There is reason that e.g. C# does not allow it.

                                    kshegunovK 1 Reply Last reply
                                    0
                                    • fcarneyF Offline
                                      fcarneyF Offline
                                      fcarney
                                      wrote on last edited by
                                      #110

                                      "Within C++, there is a much smaller and cleaner language struggling to get out."
                                      ...
                                      "And no, that smaller and cleaner language is not Java or C#."
                                      Bjarne Stroustrup

                                      C++ is a perfectly valid school of magic.

                                      1 Reply Last reply
                                      0
                                      • JonBJ JonB

                                        @kshegunov
                                        But that is not my point/question. Which is: this piece of code is not the first (or the last) where someone has mistakenly written this. If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option? There is reason that e.g. C# does not allow it.

                                        kshegunovK Offline
                                        kshegunovK Offline
                                        kshegunov
                                        Moderators
                                        wrote on last edited by
                                        #111

                                        @JonB said in Recurring C++ and Qt anti-patterns:

                                        If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option?

                                        If this were a potential error, probably. Since this is almost always safe there's no reason to offer a warning.

                                        There is reason that e.g. C# does not allow it.

                                        Which is what exactly?

                                        Read and abide by the Qt Code of Conduct

                                        jsulmJ 1 Reply Last reply
                                        0
                                        • kshegunovK kshegunov

                                          @JonB said in Recurring C++ and Qt anti-patterns:

                                          If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option?

                                          If this were a potential error, probably. Since this is almost always safe there's no reason to offer a warning.

                                          There is reason that e.g. C# does not allow it.

                                          Which is what exactly?

                                          jsulmJ Offline
                                          jsulmJ Offline
                                          jsulm
                                          Lifetime Qt Champion
                                          wrote on last edited by
                                          #112

                                          @kshegunov I think the point from @JonB is that people do call static methods on an object by mistake and then wander why the object is not changed (I sometimes see this here in the forums). The compiler could generate a warning, but I doubt people would care enough about those if they do not even notice what they do wrongly :-)

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

                                          J.HilkJ kshegunovK 2 Replies Last reply
                                          1

                                          • Login

                                          • Login or register to search.
                                          • First post
                                            Last post
                                          0
                                          • Categories
                                          • Recent
                                          • Tags
                                          • Popular
                                          • Users
                                          • Groups
                                          • Search
                                          • Get Qt Extensions
                                          • Unsolved