Fix Geant4 random number initialisation

sim/transport/gconfig/g4Config.C

@@ -62,8 +62,10 @@ void Config()
 
 
   //set geant4 specific stuff
+  // Get the infomation about the seed value defined by SetSeed from the base class.
+  // Since ROOT 6.24 the derived classes return a differnt value.
   Text_t buffer[50];
-  sprintf(buffer, "/random/setSeeds %i  %i ", gRandom->GetSeed(), gRandom->GetSeed());
+  sprintf(buffer, "/random/setSeeds %i  %i ", gRandom->TRandom::GetSeed(), gRandom->TRandom::GetSeed());
   geant4->ProcessGeantCommand(buffer);
 
   geant4->SetMaxNStep(10000);  // default is 30000

sim/transport/steer/CbmGeant4Settings.cxx

@@ -34,8 +34,11 @@ void CbmGeant4Settings::Init(TVirtualMC* vmc)
   // --- Random seed and maximum number of steps
   size_t buf_size = 100;
   Text_t buffer[buf_size];
-  int result_length =
-    snprintf(buffer, buf_size - 1, "/random/setSeeds %i  %i ", gRandom->GetSeed(), gRandom->GetSeed());
+  // Get the infomation about the seed value defined by SetSeed from the base class.
+  // Since ROOT 6.24 the derrived classes return a differnt value.
+  fRandomSeed = gRandom->TRandom::GetSeed();
+  LOG(info) << "Set Geant4 random seed to " << fRandomSeed;
+  int result_length = snprintf(buffer, buf_size - 1, "/random/setSeeds %i  %i ", fRandomSeed, fRandomSeed);
   if (!(result_length > 0 && result_length < static_cast<int>(buf_size))) {
     LOG(fatal) << "Buffer overrun. Random seed for Geant4 would be improper.";
   }

sim/transport/steer/CbmGeant4Settings.h

@@ -55,6 +55,12 @@ public:
    **/
   std::array<std::string, 3> GetG4RunConfig() { return fG4RunConfig; }
 
+  /** @brief Get the Geant4 random seed
+   ** @return Initial seed value
+   **
+   **/
+  Int_t GetG4Seed() { return fRandomSeed; }
+
   /** @brief Set a new command which should be passsed to Geant4. The call will
    ** remove the current list of commands
    ** @param[in] Geant4 command string
@@ -71,12 +77,23 @@ public:
    **/
   void AddG4Command(std::string command) { fG4Commands.push_back(command); }
 
+  /** @brief Get the Geant4 commands
+   ** @return Vector with the commands passed to Geant4 
+   **
+   **/
+  std::vector<std::string> GetG4Commands() { return fG4Commands; }
+
   /** @brief Set the maximum number of steps after which the transport is stopped
    ** list of commands
    ** @param[in] Number of steps
    **/
   void SetMaximumNumberOfSteps(Int_t numSteps) { fMaxNumSteps = numSteps; }
 
+  /** @brief Get the maximum number of steps
+   ** @return Number of steps after which the transport is stopped
+   **/
+  Int_t GetMaximumNumberOfSteps() { return fMaxNumSteps; }
+
 private:
   std::array<std::string, 3> fG4RunConfig {{"geomRoot", "QGSP_BERT_EMV+optical", "stepLimiter"}};
 
@@ -90,7 +107,9 @@ private:
 
   Int_t fMaxNumSteps {10000000};
 
-  ClassDef(CbmGeant4Settings, 3);
+  Int_t fRandomSeed {0};
+
+  ClassDef(CbmGeant4Settings, 4);
 };
 
 #endif /* CBMGEANT4SETTINGS_H */