Hi,

l want to load dynamically DLL ( instrument driver) so l can change on the fly which driver to use for my instruments.

The DLL contains a QDialog with a specific class containing all driver's commands. Overall works very well except when l change the DLL, can not open the Qdialog ( .exec() ), it crash.

the driver/ dll are tested individually and works fine.

I suspect something on class allocation below, but can not figure it out.


here is the code below:
- first copy the .dll to a specific name so can use same the driver multiple times in the application.
- then load teh class containing the GPIB commands
- then load the class for the Qdialog ( UI)

Qt Code: 
  1. short GPIB_Dashboard::Load_Drivers_Vds_1(QString *error_msg)
  2. {
  3.     QString drivername;
  4.     QString error;
  5.     QStringList message;
  6.     {
  7.         if(My_Vds1_Lib != NULL)
  8.         {
  9.             My_Vds1_Lib->unload();
  10.             delete My_Vds1_Lib;
  11.             My_Vds1_Lib = new QLibrary();
  12.         }
  13.         else
  14.             My_Vds1_Lib = new QLibrary();
  15.  
  16.  
  17.         //reserve DLL copy
  18.         drivername = QCoreApplication::applicationDirPath()+"//Driver_Vds1.dll";
  19.         if(QFile::exists(drivername))
  20.             if(!QFile::remove(drivername))
  21.             {
  22.                 QTextStream(error_msg) << "error: could not image driver Vds1";
  23.                 return 1;
  24.             }
  25.         if(!QFile::copy(Vds1.name,drivername ))
  26.         {
  27.             QTextStream(error_msg) <<"error: could not copy driver Vds1";
  28.             return 1;
  29.         }
  30.  
  31.         My_Vds1_Lib->setFileName(drivername);
  32.         My_Vds1_Lib->load();
  33.  
  34.  
  35.         DCsource_Vds1_class = (My_DCsource_Prototype) My_Vds1_Lib->resolve("CreateDCSourceClass");
  36.         if(!DCsource_Vds1_class){
  37.             //   DCsource_1_online = 0;
  38.             QTextStream(error_msg) <<"Vds1 driver: class unresolved";
  39.             return 1;
  40.         }
  41.         DCsource_Vds1 = DCsource_Vds1_class();
  42.         DCsource_Vds1->Instance_name = "Vds1";
  43.         DCsource_Vds1->LoadConfig();
  44.         DCsource_Vds1->Read_GPIB_config(&message, &error);
  45.  
  46.         My_Dlg_Vds1_Class= NULL;
  47.         Dlg_DCsource_Vds1 = NULL;
  48.         My_Dlg_Vds1_Class = (Dlg_DCSource_Prototype) My_Vds1_Lib->resolve("CreateDCSourceDialogClass");
  49.         if(!My_Dlg_Vds1_Class){
  50.             //   DCsource_1_online = 0;
  51.             QTextStream(error_msg) <<"Vds1 driver: class unresolved";
  52.             return 1;
  53.         }
  54.         //     My_Vds1_Lib->unload();
  55.  
  56.         Dlg_DCsource_Vds1 = My_Dlg_Vds1_Class(DCsource_Vds1);
  57.  
  58.         QTextStream(error_msg) <<"Vds1 driver: successfully loaded";
  59.     }
  60.  
  61.     return 0;
  62. }
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am l missing something ?