How to know where on device my application is installed.

As you may want to provide user to install you application both on phone memory (C:\) OR on memory Card (E:\) So when try to access your data files you may require to find out which drive your application is installed.

Pre-v9 SDK suppoerted devices.

   TFileName fullPath(fileName);
   CompleteWithAppPath(fullPath);    // from aknutils.h
   // fullPath now will contain <drive>:\system\apps\<application_name>

v9.x SDK suppoerted devices.

    TFileName appPath;
   TBuf<2> appDrive;
   // Returns private path of this application
   // in following format: \Private\<SID of the application>\
   // (does not contain drive specification).
   iEikonEnv->FsSession().PrivatePath( appPath );
   // Extract drive letter into appDrive
   appDrive.Copy(iEikonEnv->EikAppUi()->Application()->AppFullName().Left(2));
   // Insert drive letter into path
   appPath.Insert(0, appDrive);