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The missing startDetached overloaded function

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  • A Offline
    A Offline
    Aman Jiang
    wrote on last edited by
    #1

    QProcess has these static overloaded functions:

    bool startDetached(const QString & program, const QStringList & arguments, const QString & workingDirectory, qint64 * pid = 0);
    bool startDetached(const QString & program, const QStringList & arguments);
    bool startDetached(const QString & program);

    But this one is missing:

    bool startDetached(const QString & program, const QString & workingDirectory, qint64 * pid = 0);

    And you can't just use a QProcess object to do this, because a member function named 'detach' is also missing.

    :-(

    1 Reply Last reply
    0
    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by SGaist
      #2

      Hi,

      Why not pass an empty QStringList for the arguments parameter ?

      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
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      • A Offline
        A Offline
        Aman Jiang
        wrote on last edited by
        #3

        I tried, it didn't work, because startDetached expects arguments will in arguments but it's not, I guess.

        jsulmJ 1 Reply Last reply
        0
        • A Aman Jiang

          I tried, it didn't work, because startDetached expects arguments will in arguments but it's not, I guess.

          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #4

          @Aman-Jiang No, arguments list can be empty, QProcess doesn't care whether the executable you want to start expects any parameters or not. You should check why it didn't work.

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

          A 1 Reply Last reply
          0
          • jsulmJ jsulm

            @Aman-Jiang No, arguments list can be empty, QProcess doesn't care whether the executable you want to start expects any parameters or not. You should check why it didn't work.

            A Offline
            A Offline
            Aman Jiang
            wrote on last edited by
            #5

            @jsulm Are you sure ?

            On Windows 10, Visual Studio 2013, Qt5.5.1, this code will open notepad:

            QProcess::startDetached("notepad.exe", QStringList(), R"(C:\Users\Aman\Desktop)");
            

            And this, nothing happened:

            QProcess::startDetached("notepad.exe a.txt", QStringList(), R"(C:\Users\Aman\Desktop)");
            

            There is exactly a txt file called 'a.txt' exists in 'C:\Users\Aman\Desktop' directory but this is not the point, the point is that notepad is not started, you know notepad can starts with error arguments.

            jsulmJ 1 Reply Last reply
            0
            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #6

              Because your calling it wrong. a.text is an argument so put it in the argument list.

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

              A 2 Replies Last reply
              0
              • A Aman Jiang

                @jsulm Are you sure ?

                On Windows 10, Visual Studio 2013, Qt5.5.1, this code will open notepad:

                QProcess::startDetached("notepad.exe", QStringList(), R"(C:\Users\Aman\Desktop)");
                

                And this, nothing happened:

                QProcess::startDetached("notepad.exe a.txt", QStringList(), R"(C:\Users\Aman\Desktop)");
                

                There is exactly a txt file called 'a.txt' exists in 'C:\Users\Aman\Desktop' directory but this is not the point, the point is that notepad is not started, you know notepad can starts with error arguments.

                jsulmJ Offline
                jsulmJ Offline
                jsulm
                Lifetime Qt Champion
                wrote on last edited by
                #7

                @Aman-Jiang Yes, I'm sure. What I mean is: if you don't have any parameters then the list can be empty. Your second example is wrong: if you have any parameters then put them in the list:

                QProcess::startDetached("notepad.exe", QStringList() << "a.txt", R"(C:\Users\Aman\Desktop)");
                

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

                A 1 Reply Last reply
                0
                • SGaistS SGaist

                  Because your calling it wrong. a.text is an argument so put it in the argument list.

                  A Offline
                  A Offline
                  Aman Jiang
                  wrote on last edited by
                  #8

                  @SGaist I know that.

                  This code will works fine:

                  QProcess::startDetached("notepad.exe a.txt");
                  

                  But there is no 'workdir' argument. This is what I am talking about. I need this version but it's missing:

                  bool startDetached(const QString & program, const QString & workingDirectory, qint64 * pid = 0);
                  
                  jsulmJ 1 Reply Last reply
                  0
                  • jsulmJ jsulm

                    @Aman-Jiang Yes, I'm sure. What I mean is: if you don't have any parameters then the list can be empty. Your second example is wrong: if you have any parameters then put them in the list:

                    QProcess::startDetached("notepad.exe", QStringList() << "a.txt", R"(C:\Users\Aman\Desktop)");
                    
                    A Offline
                    A Offline
                    Aman Jiang
                    wrote on last edited by
                    #9

                    @jsulm I know it's wrong, and I know how to call this function. But I don't need this version, I need this one:

                    bool startDetached(const QString & program, const QString & workingDirectory, qint64 * pid = 0);
                    

                    The program and arguments in one string, and a working dir argument.

                    I am talking about overloaded functions.

                    1 Reply Last reply
                    0
                    • A Aman Jiang

                      @SGaist I know that.

                      This code will works fine:

                      QProcess::startDetached("notepad.exe a.txt");
                      

                      But there is no 'workdir' argument. This is what I am talking about. I need this version but it's missing:

                      bool startDetached(const QString & program, const QString & workingDirectory, qint64 * pid = 0);
                      
                      jsulmJ Offline
                      jsulmJ Offline
                      jsulm
                      Lifetime Qt Champion
                      wrote on last edited by jsulm
                      #10

                      @Aman-Jiang
                      Why not use this one with empty parameter list?

                      bool startDetached(const QString & program, const QStringList & arguments, const QString & workingDirectory, qint64 * pid = 0);
                      

                      like

                      startDetached("notepad.exe", QStringList(), "c:\\temp", 123);
                      

                      I don't see any need for one more method.

                      "The program and arguments in one string" - don't do that! Arguments should be passed as arguments list.

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

                      A 1 Reply Last reply
                      1
                      • SGaistS SGaist

                        Because your calling it wrong. a.text is an argument so put it in the argument list.

                        A Offline
                        A Offline
                        Aman Jiang
                        wrote on last edited by
                        #11

                        I am working on some kind of launcher. There is many command lines from the user, these command lines is used to launch the specified programs, there're stored in db. I don't want to split these command lines into QStringList on launching, because the target programs could be very different, it's risk, I want to use them directly.

                        jsulmJ 1 Reply Last reply
                        0
                        • jsulmJ jsulm

                          @Aman-Jiang
                          Why not use this one with empty parameter list?

                          bool startDetached(const QString & program, const QStringList & arguments, const QString & workingDirectory, qint64 * pid = 0);
                          

                          like

                          startDetached("notepad.exe", QStringList(), "c:\\temp", 123);
                          

                          I don't see any need for one more method.

                          "The program and arguments in one string" - don't do that! Arguments should be passed as arguments list.

                          A Offline
                          A Offline
                          Aman Jiang
                          wrote on last edited by
                          #12

                          @jsulm This version accepts program and arguments in one string:

                          bool startDetached(const QString & program);
                          

                          You couldn't always pass arguments as arguments list, because the split rule can be different, a program may like semicolon more than space.

                          On windows, GetCommandLine returns just one string.

                          kshegunovK 1 Reply Last reply
                          0
                          • mrjjM Offline
                            mrjjM Offline
                            mrjj
                            Lifetime Qt Champion
                            wrote on last edited by
                            #13

                            @Aman-Jiang said:

                            startDetached

                            While it can work with params with the exe string
                            , it will break very easy

                            QProcess::startDetached("notepad.exe E:/space in path/test.txt");

                            wont work.

                            There is nothing stopping you from doing
                            startDetached("notepad.exe TEST.txt", QStringList(), "c:\temp");
                            to specify work dir.
                            and "misuse" the exe string with params.

                            A 1 Reply Last reply
                            1
                            • A Aman Jiang

                              I am working on some kind of launcher. There is many command lines from the user, these command lines is used to launch the specified programs, there're stored in db. I don't want to split these command lines into QStringList on launching, because the target programs could be very different, it's risk, I want to use them directly.

                              jsulmJ Offline
                              jsulmJ Offline
                              jsulm
                              Lifetime Qt Champion
                              wrote on last edited by
                              #14

                              @Aman-Jiang Are you aware that startDetach(const QString& program) splits the parameter you pass?
                              Read the documentation:

                              After the command string has been split and unquoted, this function behaves like the overload which takes the arguments as a string list.
                              

                              http://doc.qt.io/qt-5/qprocess.html#startDetached-1

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

                              A 1 Reply Last reply
                              0
                              • A Aman Jiang

                                @jsulm This version accepts program and arguments in one string:

                                bool startDetached(const QString & program);
                                

                                You couldn't always pass arguments as arguments list, because the split rule can be different, a program may like semicolon more than space.

                                On windows, GetCommandLine returns just one string.

                                kshegunovK Offline
                                kshegunovK Offline
                                kshegunov
                                Moderators
                                wrote on last edited by
                                #15

                                @Aman-Jiang

                                You couldn't always pass arguments as arguments list, because the split rule can be different, a program may like semicolon more than space.

                                You can and you should, and the split rule can't be different, so listen to the fellows that commented above and pass the arguments as a string list. You may need to do some parsing yourself to handle quoted/escaped strings, for which you can use something like boost's Spirit module. But as @mrjj noted, passing the arguments along with the executable in one string is just abuse of the API and may or may not work depending on OS/Qt version and other factors beyond your control.

                                Kind regards.

                                Read and abide by the Qt Code of Conduct

                                A 1 Reply Last reply
                                1
                                • mrjjM mrjj

                                  @Aman-Jiang said:

                                  startDetached

                                  While it can work with params with the exe string
                                  , it will break very easy

                                  QProcess::startDetached("notepad.exe E:/space in path/test.txt");

                                  wont work.

                                  There is nothing stopping you from doing
                                  startDetached("notepad.exe TEST.txt", QStringList(), "c:\temp");
                                  to specify work dir.
                                  and "misuse" the exe string with params.

                                  A Offline
                                  A Offline
                                  Aman Jiang
                                  wrote on last edited by
                                  #16

                                  @mrjj I don't get you. There is spaces in the string, without quotation marks, it's invalid command line, what do you want to prove ?

                                  1 Reply Last reply
                                  0
                                  • SGaistS Offline
                                    SGaistS Offline
                                    SGaist
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #17

                                    That it's the kind of use case you are likely going to have to fight against since you want to pass everything in a single string.

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

                                    A 1 Reply Last reply
                                    0
                                    • jsulmJ jsulm

                                      @Aman-Jiang Are you aware that startDetach(const QString& program) splits the parameter you pass?
                                      Read the documentation:

                                      After the command string has been split and unquoted, this function behaves like the overload which takes the arguments as a string list.
                                      

                                      http://doc.qt.io/qt-5/qprocess.html#startDetached-1

                                      A Offline
                                      A Offline
                                      Aman Jiang
                                      wrote on last edited by
                                      #18

                                      @jsulm No... I haven't notice this line in the document...

                                      1 Reply Last reply
                                      0
                                      • kshegunovK kshegunov

                                        @Aman-Jiang

                                        You couldn't always pass arguments as arguments list, because the split rule can be different, a program may like semicolon more than space.

                                        You can and you should, and the split rule can't be different, so listen to the fellows that commented above and pass the arguments as a string list. You may need to do some parsing yourself to handle quoted/escaped strings, for which you can use something like boost's Spirit module. But as @mrjj noted, passing the arguments along with the executable in one string is just abuse of the API and may or may not work depending on OS/Qt version and other factors beyond your control.

                                        Kind regards.

                                        A Offline
                                        A Offline
                                        Aman Jiang
                                        wrote on last edited by
                                        #19

                                        @kshegunov Okay, I get you, I know the reason now. But, If Qt's goal is make everything easier, why not add one more overloaded startDetached ? If this one:

                                        bool startDetached(const QString & program);
                                        

                                        Could do the right thing cross Qt versions and OS versions, add another one:

                                        bool startDetached(const QString & program, const QString& workDir);
                                        

                                        Is more complete. At least I think so.

                                        raven-worxR kshegunovK 2 Replies Last reply
                                        0
                                        • SGaistS SGaist

                                          That it's the kind of use case you are likely going to have to fight against since you want to pass everything in a single string.

                                          A Offline
                                          A Offline
                                          Aman Jiang
                                          wrote on last edited by
                                          #20

                                          @SGaist I used to write lots of string parsing codes, it's not very hard, but I like a more easier way to do the same work if I could.

                                          1 Reply Last reply
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