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Using the JNI with QT - Lib/DLLs are giving a file format error

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  • hskoglundH Online
    hskoglundH Online
    hskoglund
    wrote on last edited by
    #6

    Easiest is to check if you have a 32bit or 64bit installation of Java, open a CMD window and type:
    "C:\Program Files\Java\jdk1.8.0_65\bin\java.exe" -version

    You should see 3 lines, the last one tells if you have 32bit or 64bit Java.

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    • R Offline
      R Offline
      RBrNx277
      wrote on last edited by
      #7

      It gave me this response: http://i.imgur.com/WDCfFhx.png
      So I guess I do have the 64bit JNI? I'll have a look to see if there is a 32bit version. Or would it be easier to build my application as 64bit?

      Thanks for your help.

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      • hskoglundH Online
        hskoglundH Online
        hskoglund
        wrote on last edited by
        #8

        Well 64-bit is the future :-) So I think try building your app as 64-bit.
        However on Windows that requires you to have Visual Studio 2013 installed (there's no 64-bit option for the MinGW compiler :-(

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        • R Offline
          R Offline
          RBrNx277
          wrote on last edited by
          #9

          Ahh OK that makes sense. I have Visual Studio 2013 installed, is there a step by step process to compile my QT application for 64bit?

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          • hskoglundH Online
            hskoglundH Online
            hskoglund
            wrote on last edited by
            #10

            It's pretty straightforward: first run Qt's MaintenanceTool.exe app to add 64-bit Visual Studio 2013.
            Then to select 64-bit build for your project, easiest is to remove the file ending with "pro.user" (like myprogram.pro.user) and next time you start Qt Creator you should be able to select the 64-bits build.

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            • R Offline
              R Offline
              RBrNx277
              wrote on last edited by
              #11

              OK so I haven't tried to build the 64bit application yet, but I did try to download and use a 32bit Java version. I updated the .pro file to use the new Include Paths and LIBS flag:

              INCLUDEPATH += "C:/Program Files (x86)/Java/jdk1.8.0_74/include/"
              INCLUDEPATH += "C:/Program Files (x86)/Java/jdk1.8.0_74/include/win32/"
              LIBS += "C:/Program Files (x86)/Java/jre1.8.0_74/bin/client/jvm.dll"
              

              The "file format not recognized" error seems to have disappeared (yay?) but now I get the following error:

              undefined reference to `_imp__JNI_CreateJavaVM@12'
              

              I assume I'm still doing something incorrectly? My guess is using the 64bit application will also produce this error?

              I seen a few bits and pieces online about .Lib files and .a files, are they something I need?

              Thanks

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              • hskoglundH Online
                hskoglundH Online
                hskoglund
                wrote on last edited by
                #12

                Yeas you have now opened another nice can of worms. For starters you'll need a jvm.lib, here's an example Good luck!

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                • R Offline
                  R Offline
                  RBrNx277
                  wrote on last edited by
                  #13

                  Thanks for the link, it doesn't do anything differently from the way I have everything coded at the moment though. I have all the same (or similar) code to set up the JVM and call Java functions, but my project wing build because of that undefined reference error. It doesn't seem to mention anything about .lib/.a files either, do I just need to add the location of the JVM.lib to the libs flag in the .pro file? Or is there more to it?

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

                    Shouldn't this one

                    LIBS += "C:/Program Files (x86)/Java/jre1.8.0_74/bin/client/jvm.dll"
                    

                    either be

                    LIBS += -L"C:/Program Files (x86)/Java/jre1.8.0_74/bin/client" -ljvm"
                    

                    But it probably will not work in any case because you use MinGW and JRE most probably another (VS?) compiler. On Windows you cannot mix compilers.

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

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                    • R Offline
                      R Offline
                      RBrNx277
                      wrote on last edited by
                      #15

                      Aren't the -L flags only used in Linux systems? Or did I read that wrong?
                      OK so the problem might be the JVM.dll was compiled with a VS compiler and I'm trying to use it with the MinGW compiler? Is there a way to check what compiler the DLL was compiled with? Could I change the Compiler QT is using to the same one?

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                      • SGaistS Offline
                        SGaistS Offline
                        SGaist
                        Lifetime Qt Champion
                        wrote on last edited by
                        #16

                        Hi,

                        No they are not.

                        The first problem you have is that you are trying to link against a .dll which is wrong. You need the corresponding .lib file.

                        But first thing, do you need that for an Android application ?

                        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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                        • R Offline
                          R Offline
                          RBrNx277
                          wrote on last edited by
                          #17

                          Ok, I know the location of the .lib file, what should I do with it?

                          No this is just a regular windows application. There's a piece of code I'd like to use which is written in Java, I will perhaps look to convert it to C++ in the future but for now I'd just like to use the exisiting Java code.

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                          • SGaistS Offline
                            SGaistS Offline
                            SGaist
                            Lifetime Qt Champion
                            wrote on last edited by
                            #18

                            Follow the example that @jsulm provided:

                            LIBS += -L"C:/Path/to/Java/libs/" -ljvm"

                            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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                            • R Offline
                              R Offline
                              RBrNx277
                              wrote on last edited by
                              #19

                              Nice one, thank you! Finally managed to get it working by only using these three lines in my .pro file

                              INCLUDEPATH += "C:/Program Files (x86)/Java/jdk1.8.0_74/include/"
                              INCLUDEPATH += "C:/Program Files (x86)/Java/jdk1.8.0_74/include/win32/"
                              LIBS += -L"C:/Program Files (x86)/Java/jdk1.8.0_74/lib/" -ljvm
                              

                              and also by placing the JVM.dll where the .exe file is built by QT.

                              Unfortunately my program now crashes when it attempts to create a VM for Java and says

                              Error occurred during initialization of VM
                              Unable to load native library: Can't find dependent libraries
                              

                              But I guess that's a different problem!

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                              • jsulmJ Offline
                                jsulmJ Offline
                                jsulm
                                Lifetime Qt Champion
                                wrote on last edited by
                                #20

                                It looks like the jvm DLL depends on at least one more DLL. You can use DependencyWalker to check which dependencies you have.

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

                                R 1 Reply Last reply
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                                • jsulmJ jsulm

                                  It looks like the jvm DLL depends on at least one more DLL. You can use DependencyWalker to check which dependencies you have.

                                  R Offline
                                  R Offline
                                  RBrNx277
                                  wrote on last edited by
                                  #21

                                  @jsulm I tried using the DependencyWalker on the JVM.dll, but it gave me some very strange results. I got a LOT of missing DLLs for things like API-MS-WIN-*.dll as you can see from the images here: http://imgur.com/a/h1CvW

                                  There doesn't seem to be any other DLLs missing as far as I can tell.

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                                  • hskoglundH Online
                                    hskoglundH Online
                                    hskoglund
                                    wrote on last edited by
                                    #22

                                    Hi maybe not a missing DLL, but perhaps too many, it could be because you have more than one version of Java installed (32-bit and 64-bit).

                                    Either uninstall all the Java versions you can find on your PC and reinstall just the one you need.

                                    Or you can try to change the PATH env. variable so that the first entry in it points to your correct Java version, open a CMD window:
                                    PATH = "C:\Program Files (x86)\Java\jre1.8.0_74\bin\client";%PATH%

                                    and try to start your app from that CMD window.

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                                    • R Offline
                                      R Offline
                                      RBrNx277
                                      wrote on last edited by
                                      #23

                                      I just tried doing that, however my program will not run outside of QT for some reason? If I click the run button in QT the program executes fine (but then gives me the JVM error as before), but if I run the program from the command line or by double clicking on it I get an error saying:

                                      The procedure entry point __cxa_throw_bad_array_new_length could not be located in the dynamic link library D:\My Documents\Qt Projects\build-PROGRAM-Desktop_Qt_5_5_1_MinGW_32bit-Release\debug\Qt5Core.dll
                                      

                                      I have also tried it with the release version of my program but I get the same error.

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                                      • hskoglundH Online
                                        hskoglundH Online
                                        hskoglund
                                        wrote on last edited by
                                        #24

                                        Hi I think that error occurs because you copied the wrong Qt5Core.dll (from Qt Creators' bin directory) instead of the one in C:\Qt\5.5\mingw492_32\bin. Instead of copying manually, you could try windeployqt on your .exe file.

                                        R 1 Reply Last reply
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                                        • hskoglundH hskoglund

                                          Hi I think that error occurs because you copied the wrong Qt5Core.dll (from Qt Creators' bin directory) instead of the one in C:\Qt\5.5\mingw492_32\bin. Instead of copying manually, you could try windeployqt on your .exe file.

                                          R Offline
                                          R Offline
                                          RBrNx277
                                          wrote on last edited by
                                          #25

                                          @hskoglund I just deleted all the .dlls in my folder and copied
                                          libgcc_s_dw2-1.dll
                                          libwinpthread-1.dll
                                          Qt5Cored.dll
                                          Qt5GUId.dll
                                          Qt5Widgetsd.dll

                                          from the C:\Qt\5.5\mingw492_32\bin
                                          into the folder where my .exe file is, unfortunately I still get the same entry point error.

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