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Writing to the standard input of a process

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  • A Offline
    A Offline
    A1exander_Z
    wrote on last edited by
    #10

    Yes, adding process->waitForStarted() before process->write("test\n") does not change anything, the process does not terminate if there is no process->waitForFinished() line in the end. Closing (or not closing) the write channel has no effect in all cases.

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    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #11

      I just forgot one basic question… What version of Qt are you using on what version of Windows ?

      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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      • A Offline
        A Offline
        A1exander_Z
        wrote on last edited by
        #12

        Qt 5.2.0 on Windows 7 Ultimate 64 bit, Service Pack 1.

        I have tried to build my program using two compilers, MinGW 32 bit and MSVC2012 64 bit. The behavior is the same in both cases.

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

          Does it also happen if you call a standard cmd command ?

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          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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          • A Offline
            A Offline
            A1exander_Z
            wrote on last edited by
            #14

            I am not sure how to call a standard cmd command from a Qt application (I have tried process->setProgram("dir"), it runs but produces no output to stdout), but I did further research.

            I wrote a simple program in C++ and compiled it with MinGW:

            @#include <iostream>
            #include <string>

            int main(int argc, char *argv[])
            {
            std::string s;
            std::cin >> s;
            std::cout << s << std::endl;
            }@

            It works both with and without process->waitForFinished() call, my Qt application can write to its standard input and retreive echoed string from its output. Writing from a slot connected to the 'QProsess::started' signal also works. It seems that the problem is with my C# program after all.

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

              Did you try with a similar minimal application written in C# ?

              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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              • A Offline
                A Offline
                A1exander_Z
                wrote on last edited by
                #16

                Yes, I have tried this:

                @class Program
                {
                static int Main(string[] args)
                {
                string s;
                s = Console.ReadLine();
                Console.WriteLine(s);
                return 0;
                }
                }@

                Works if I place waitForFinished() call after writing to the standard input of the process, but never terminates without it. Changing configuration of the C# program from Debug to Release in Visual Studio does not help.

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                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #17

                  Maybe a silly question (I don't know much about C#) but aren't you missing a "\n" here ?

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                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  • A Offline
                    A Offline
                    A1exander_Z
                    wrote on last edited by
                    #18

                    No, Console.WriteLine() method inserts it automatically. And with waitForFinished() call it works even when I change Console.WriteLine() to Console.Write(), which does not insert a newline symbol.

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #19

                      Could there be some subtle difference on how the C# runtime uses stdin/stdout ?

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                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • A Offline
                        A Offline
                        A1exander_Z
                        wrote on last edited by
                        #20

                        Yes, it seems that there is some difference, but I am not a C# expert and I have no idea what it is. I will try a simple program compiled using Mono but for now, I think it is easier to send all data as command line parameters.

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                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #21

                          As long as it's clean and works, do what is best.

                          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

                          M 1 Reply Last reply
                          0
                          • SGaistS SGaist

                            As long as it's clean and works, do what is best.

                            Happy Coding !

                            M Offline
                            M Offline
                            mhmdkanj
                            wrote on last edited by
                            #22

                            @SGaist I am currently having the same issue for C# executables and writing to their standard input. Assuming that I cannot change the C# code, how would I fix this in Qt in case you can enlighten me after a few years.. Many thanks!

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                            • SGaistS Offline
                              SGaistS Offline
                              SGaist
                              Lifetime Qt Champion
                              wrote on last edited by
                              #23

                              hi,

                              Did you apply the same technique as @A1exander_Z did ?

                              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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