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Writing to the standard input of a process

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  • SGaistS Offline
    SGaistS Offline
    SGaist
    Lifetime Qt Champion
    wrote on last edited by
    #9

    Does it also happen if you add waitForStarted before writing to it ?

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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
      #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 ?

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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
          #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# ?

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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
                  #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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                    • 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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                        • 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
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                            • 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 ?

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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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