| Geant4 User's Guide For Application Developers Communication and Control

7.2 User Interface - Defining New Commands

## 7.2.1 G4UImessenger

G4UImessenger is a base class which represents a messenger that delivers command(s) to the destination class object. Your concrete messenger should have the following functionalities.

- Construct your command(s) in the constructor of your messenger.
- Destruct your command(s) in the destructor of your messenger.

These requirements mean that your messenger should keep all pointers to your command objects as its data members.

You can use G4UIcommand derived classes for the most frequent types of command. These derived classes have their own conversion methods according to their types, and they make implementation of the `SetNewValue()` and `GetCurrentValue()` methods of your messenger much easier and simpler.

For complicated commands which take various parameters, you can use the G4UIcommand base class, and construct G4UIparameter objects by yourself. You don't need to delete G4UIparameter object(s).

In the `SetNewValue()` and `GetCurrentValue()` methods of your messenger, you can compare the G4UIcommand pointer given in the argument of these methods with the pointer of your command, because your messenger keeps the pointers to the commands. Thus, you don't need to compare by command name. Please remember, in the cases where you use G4UIcommand derived classes, you should store the pointers with the types of these derived classes so that you can use methods defined in the derived classes according to their types without casting.

G4UImanager/G4UIcommand/G4UIparameter have very powerful type and range checking routines. You are strongly recommended to set the range of your parameters. For the case of a numerical value (`int` or `double`), the range can be given by a G4String using C++ notation, e.g., `"X > 0 && X < 10"`. For the case of a string type parameter, you can set a candidate list. Please refer to the detailed descriptions below.

`GetCurrentValue()` will be invoked after the user's application of the corresponding command, and before the `SetNewValue()` invocation. This `GetCurrentValue()` method will be invoked only if

- at least one parameter of the command has a range
- at least one parameter of the command has a candidate list
- at least the value of one parameter is omitted and this parameter is defined as omittable and `currentValueAsDefault`

For the first two cases, you can re-set the range or the candidate list if you need to do so, but these ``re-set'' parameters are needed only for the case where the range or the candidate list varies dynamically.

A command can be ``state sensitive'', i.e., the command can be accepted only for a certain G4ApplicationState(s). For example, the `/run/beamOn` command should not be accepted when Geant4 is processing another event (``G4State_EventProc'' state). You can set the states available for the command with the `AvailableForStates()` method.

## 7.2.2 G4UIcommand and its derived classes

Methods available for all derived classes

  These are methods defined in the G4UIcommand base class which should be used from the derived classes.

  - `void SetGuidance(char*)`

    Define a guidance line. You can invoke this method as many times as you need to give enough amount of guidance. Please note that the first line will be used as a title head of the command guidance.

  - `void availableForStates(G4ApplicationState s1,...)`

    If your command is valid only for certain states of the Geant4 kernel, specify these states by this method. Currently available states are `G4State_PreInit, G4State_Init, G4State_Idle, G4State_GeomClosed,` and `G4State_EventProc`. Refer to the section 3.4.2 for meaning of each state. Please note that the `Pause` state had been removed from G4ApplicationState.

  - `void SetRange(char* range)`

    Define a range of the parameter(s). Use C++ notation, e.g., `"x > 0 && x < 10"`, with variable name(s) defined by the `SetParameterName()` method. For the case of a G4ThreeVector, you can set the relation between parameters, e.g., `"x > y"`.

G4UIdirectory

  This is a G4UIcommand derived class for defining a directory.

  - `G4UIdirectory(char* directoryPath)`

    Constructor. Argument is the (full-path) directory, which must begin and terminate with ``/`'.

G4UIcmdWithoutParameter

  This is a G4UIcommand derived class for a command which takes no parameter.

  - `G4UIcmdWithoutParameter(char* commandPath,G4UImessenger* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

G4UIcmdWithABool

  This is a G4UIcommand derived class which takes one boolean type parameter.

  - `G4UIcmdWithABool(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName(char* paramName,G4bool omittable)`

    Define the name of the boolean parameter and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(G4bool defVal)`

    Define the default value of the boolean parameter.

  - `G4bool GetNewBoolValue(G4String paramString)`

    Convert G4String parameter value given by the `SetNewValue()` method of your messenger into boolean.

  - `G4String convertToString(G4bool currVal)`

    Convert the current boolean value to G4String which should be returned by the `GetCurrentValue()` method of your messenger.

G4UIcmdWithAnInteger

  This is a G4UIcommand derived class which takes one integer type parameter.

  - `G4UIcmdWithAnInteger(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName(char* paramName,G4bool omittable)`

    Define the name of the integer parameter and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(G4int defVal)`

    Define the default value of the integer parameter.

  - `G4int GetNewIntValue(G4String paramString)`

    Convert G4String parameter value given by the `SetNewValue()` method of your messenger into integer.

  - `G4String convertToString(G4int currVal)`

    Convert the current integer value to G4String, which should be returned by the `GetCurrentValue()` method of your messenger.

G4UIcmdWithADouble

  This is a G4UIcommand derived class which takes one double type parameter.

  - `G4UIcmdWithADouble(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName(char* paramName,G4bool omittable)`

    Define the name of the double parameter and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(G4double defVal)`

    Define the default value of the double parameter.

  - `G4double GetNewDoubleValue(G4String paramString)`

    Convert G4String parameter value given by the `SetNewValue()` method of your messenger into double.

  - `G4String convertToString(G4double currVal)`

    Convert the current double value to G4String which should be returned by the `GetCurrentValue()` method of your messenger.

G4UIcmdWithAString

  This is a G4UIcommand derived class which takes one string type parameter.

  - `G4UIcmdWithAString(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName(char* paramName,G4bool omittable)`

    Define the name of the string parameter and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(char* defVal)`

    Define the default value of the string parameter.

  - `void SetCandidates(char* candidateList)`

    Define a candidate list which can be taken by the parameter. Each candidate listed in this list should be separated by a single space. If this candidate list is given, a string given by the user but which is not listed in this list will be rejected.

G4UIcmdWith3Vector

  This is a G4UIcommand derived class which takes one three vector parameter.

  - `G4UIcmdWith3Vector(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName`
    `(char* paramNamX,char* paramNamY,char* paramNamZ,G4bool omittable)`

    Define the names of each component of the three vector and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(G4ThreeVector defVal)`

    Define the default value of the three vector.

  - `G4ThreeVector GetNew3VectorValue(G4String paramString)`

    Convert the G4String parameter value given by the `SetNewValue()` method of your messenger into a G4ThreeVector.

  - `G4String convertToString(G4ThreeVector currVal)`

    Convert the current three vector to G4String, which should be returned by the `GetCurrentValue()` method of your messenger.

G4UIcmdWithADoubleAndUnit

  This is a G4UIcommand derived class which takes one double type parameter and its unit.

  - `G4UIcmdWithADoubleAndUnit(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName(char* paramName,G4bool omittable)`

    Define the name of the double parameter and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(G4double defVal)`

    Define the default value of the double parameter.

  - `void SetUnitCategory(char* unitCategory)`

    Define acceptable unit category.

  - `void SetDefaultUnit(char* defUnit)`

    Define the default unit. Please use this method and the `SetUnitCategory()` method alternatively.

  - `G4double GetNewDoubleValue(G4String paramString)`

    Convert G4String parameter value given by the `SetNewValue()` method of your messenger into double. Please note that the return value has already been multiplied by the value of the given unit.

  - `G4double GetNewDoubleRawValue(G4String paramString)`

    Convert G4String parameter value given by the `SetNewValue()` method of your messenger into double but without multiplying the value of the given unit.

  - `G4double GetNewUnitValue(G4String paramString)`

    Convert G4String unit value given by the `SetNewValue()` method of your messenger into double.

  - `G4String convertToString(G4bool currVal,char* unitName)`

    Convert the current double value to a G4String, which should be returned by the `GetCurrentValue()` method of your messenger. The double value will be divided by the value of the given unit and converted to a string. Given unit will be added to the string.

G4UIcmdWith3VectorAndUnit

  This is a G4UIcommand derived class which takes one three vector parameter and its unit.

  - `G4UIcmdWith3VectorAndUnit(char* commandpath,G4UImanager* theMessenger)`

    Constructor. Arguments are the (full-path) command name and the pointer to your messenger.

  - `void SetParameterName`
    `(char* paramNamX,char* paramNamY,char* paramNamZ,G4bool omittable)`

    Define the names of each component of the three vector and set the omittable flag. If omittable is true, you should define the default value using the next method.

  - `void SetDefaultValue(G4ThreeVector defVal)`

    Define the default value of the three vector.

  - `void SetUnitCategory(char* unitCategory)`

    Define acceptable unit category.

  - `void SetDefaultUnit(char* defUnit)`

    Define the default unit. Please use this method and the `SetUnitCategory()` method alternatively.

  - `G4ThreeVector GetNew3VectorValue(G4String paramString)`

    Convert a G4String parameter value given by the `SetNewValue()` method of your messenger into a G4ThreeVector. Please note that the return value has already been multiplied by the value of the given unit.

  - `G4ThreeVector GetNew3VectorRawValue(G4String paramString)`

    Convert a G4String parameter value given by the `SetNewValue()` method of your messenger into three vector, but without multiplying the value of the given unit.

  - `G4double GetNewUnitValue(G4String paramString)`

    Convert a G4String unit value given by the `SetNewValue()` method of your messenger into a double.

  - `G4String convertToString(G4ThreeVector currVal,char* unitName)`

    Convert the current three vector to a G4String which should be returned by the `GetCurrentValue()` method of your messenger. The three vector value will be divided by the value of the given unit and converted to a string. Given unit will be added to the string.

Additional comments on the `SetParameterName()` method

  You can add one additional argument of `G4bool` type for every `SetParameterName()` method mentioned above. This additional argument is named `currentAsDefaultFlag` and the default value of this argument is `false`. If you assign this extra argument as `true`, the default value of the parameter will be overriden by the current value of the target class.

## 7.2.3 An example messenger

This example is of G4ParticleGunMessenger, which is made by inheriting G4UIcommand.

    #ifndef G4ParticleGunMessenger_h
    #define G4ParticleGunMessenger_h 1

    class G4ParticleGun;
    class G4ParticleTable;
    class G4UIcommand;
    class G4UIdirectory;
    class G4UIcmdWithoutParameter;
    class G4UIcmdWithAString;
    class G4UIcmdWithADoubleAndUnit;
    class G4UIcmdWith3Vector;
    class G4UIcmdWith3VectorAndUnit;

    #include "G4UImessenger.hh"
    #include "globals.hh"

    class G4ParticleGunMessenger: public G4UImessenger
    {
      public:
        G4ParticleGunMessenger(G4ParticleGun * fPtclGun);
        ~G4ParticleGunMessenger();

      public:
        void SetNewValue(G4UIcommand * command,G4String newValues);
        G4String GetCurrentValue(G4UIcommand * command);

      private:
        G4ParticleGun * fParticleGun;
        G4ParticleTable * particleTable;

      private: //commands
        G4UIdirectory *             gunDirectory;
        G4UIcmdWithoutParameter *   listCmd;
        G4UIcmdWithAString *        particleCmd;
        G4UIcmdWith3Vector *        directionCmd;
        G4UIcmdWithADoubleAndUnit * energyCmd;
        G4UIcmdWith3VectorAndUnit * positionCmd;
        G4UIcmdWithADoubleAndUnit * timeCmd;

    };

    #endif
Source listing 7.2.1 An example of `G4ParticleGunMessenger.hh`.

    #include "G4ParticleGunMessenger.hh"
    #include "G4ParticleGun.hh"
    #include "G4Geantino.hh"
    #include "G4ThreeVector.hh"
    #include "G4ParticleTable.hh"
    #include "G4UIdirectory.hh"
    #include "G4UIcmdWithoutParameter.hh"
    #include "G4UIcmdWithAString.hh"
    #include "G4UIcmdWithADoubleAndUnit.hh"
    #include "G4UIcmdWith3Vector.hh"
    #include "G4UIcmdWith3VectorAndUnit.hh"
    #include <iostream.h>

    G4ParticleGunMessenger::G4ParticleGunMessenger(G4ParticleGun * fPtclGun)
    :fParticleGun(fPtclGun)
    {
      particleTable = G4ParticleTable::GetParticleTable();

      gunDirectory = new G4UIdirectory("/gun/");
      gunDirectory->SetGuidance("Particle Gun control commands.");

      listCmd = new G4UIcmdWithoutParameter("/gun/list",this);
      listCmd->SetGuidance("List available particles.");
      listCmd->SetGuidance(" Invoke G4ParticleTable.");

      particleCmd = new G4UIcmdWithAString("/gun/particle",this);
      particleCmd->SetGuidance("Set particle to be generated.");
      particleCmd->SetGuidance(" (geantino is default)");
      particleCmd->SetParameterName("particleName",true);
      particleCmd->SetDefaultValue("geantino");
      G4String candidateList;
      G4int nPtcl = particleTable->entries();
      for(G4int i=0;i<nPtcl;i++)
      {
        candidateList += particleTable->GetParticleName(i);
        candidateList += " ";
      }
      particleCmd->SetCandidates(candidateList);

      directionCmd = new G4UIcmdWith3Vector("/gun/direction",this);
      directionCmd->SetGuidance("Set momentum direction.");
      directionCmd->SetGuidance("Direction needs not to be a unit vector.");
      directionCmd->SetParameterName("Px","Py","Pz",true,true);
      directionCmd->SetRange("Px != 0 || Py != 0 || Pz != 0");

      energyCmd = new G4UIcmdWithADoubleAndUnit("/gun/energy",this);
      energyCmd->SetGuidance("Set kinetic energy.");
      energyCmd->SetParameterName("Energy",true,true);
      energyCmd->SetDefaultUnit("GeV");
      energyCmd->SetUnitCandidates("eV keV MeV GeV TeV");

      positionCmd = new G4UIcmdWith3VectorAndUnit("/gun/position",this);
      positionCmd->SetGuidance("Set starting position of the particle.");
      positionCmd->SetParameterName("X","Y","Z",true,true);
      positionCmd->SetDefaultUnit("cm");
      positionCmd->SetUnitCandidates("micron mm cm m km");

      timeCmd = new G4UIcmdWithADoubleAndUnit("/gun/time",this);
      timeCmd->SetGuidance("Set initial time of the particle.");
      timeCmd->SetParameterName("t0",true,true);
      timeCmd->SetDefaultUnit("ns");
      timeCmd->SetUnitCandidates("ns ms s");

      // Set initial value to G4ParticleGun
      fParticleGun->SetParticleDefinition( G4Geantino::Geantino() );
      fParticleGun->SetParticleMomentumDirection( G4ThreeVector(1.0,0.0,0.0) );
      fParticleGun->SetParticleEnergy( 1.0*GeV );
      fParticleGun->SetParticlePosition(G4ThreeVector(0.0*cm, 0.0*cm, 0.0*cm));
      fParticleGun->SetParticleTime( 0.0*ns );
    }

    G4ParticleGunMessenger::~G4ParticleGunMessenger()
    {
      delete listCmd;
      delete particleCmd;
      delete directionCmd;
      delete energyCmd;
      delete positionCmd;
      delete timeCmd;
      delete gunDirectory;
    }

    void G4ParticleGunMessenger::SetNewValue(
      G4UIcommand * command,G4String newValues)
    {
      if( command==listCmd )
      { particleTable->dumpTable(); }
      else if( command==particleCmd )
      {
        G4ParticleDefinition* pd = particleTable->findParticle(newValues);
        if(pd != NULL)
        { fParticleGun->SetParticleDefinition( pd ); }
      }
      else if( command==directionCmd )
      { fParticleGun->SetParticleMomentumDirection(directionCmd->
         GetNew3VectorValue(newValues)); }
      else if( command==energyCmd )
      { fParticleGun->SetParticleEnergy(energyCmd->
         GetNewDoubleValue(newValues)); }
      else if( command==positionCmd )
      { fParticleGun->SetParticlePosition(
         directionCmd->GetNew3VectorValue(newValues)); }
      else if( command==timeCmd )
      { fParticleGun->SetParticleTime(timeCmd->
         GetNewDoubleValue(newValues)); }
    }

    G4String G4ParticleGunMessenger::GetCurrentValue(G4UIcommand * command)
    {
      G4String cv;

      if( command==directionCmd )
      { cv = directionCmd->ConvertToString(
         fParticleGun->GetParticleMomentumDirection()); }
      else if( command==energyCmd )
      { cv = energyCmd->ConvertToString(
         fParticleGun->GetParticleEnergy(),"GeV"); }
      else if( command==positionCmd )
      { cv = positionCmd->ConvertToString(
         fParticleGun->GetParticlePosition(),"cm"); }
      else if( command==timeCmd )
      { cv = timeCmd->ConvertToString(
         fParticleGun->GetParticleTime(),"ns"); }
      else if( command==particleCmd )
      { // update candidate list
        G4String candidateList;
        G4int nPtcl = particleTable->entries();
        for(G4int i=0;i<nPtcl;i++)
        {
          candidateList += particleTable->GetParticleName(i);
          candidateList += " ";
        }
        particleCmd->SetCandidates(candidateList);
      }
      return cv;
    }
Source listing 7.2.2 An example of `G4ParticleGunMessenger.cc`.

## 7.2.4 How to control the output of G4cout/G4cerr

Instead of cout and cerr, Geant4 uses G4cout and G4cerr. Output streams from G4cout/G4cerr are handled by G4UImanager which allows the application programmer to control the flow of the stream. Output strings may therefore be displayed on another window or stored in a file. This is accomplished as follows:

1. Derive a class from G4UIsession and implement the two methods:

             G4int ReceiveG4cout(G4String coutString);
             G4int ReceiveG4cerr(G4String cerrString);

   These methods receive the string stream of G4cout and G4cerr, respectively. The string can be handled to meet specific requirements. The following sample code shows how to make a log file of the output stream:

               ostream logFile;
               logFile.open("MyLogFile");
               G4int MySession::ReceiveG4cout(G4String coutString)
               {
                 logFile << coutString << flush;
                 return 0;
               }

2. Set the destination of G4cout/G4cerr using `G4UImanager::SetCoutDestination(session)`.

   Typically this method is invoked from the constructor of G4UIsession and its derived classes, such as G4UIGAG/G4UIteminal. This method sets the destination of G4cout/G4cerr to the session. For example, when the following code appears in the constructor of G4UIterminal, the method `SetCoutDestination(this)` tells UImanager that this instance of G4UIterminal receives the stream generated by G4cout.

       	G4UIterminal::G4UIterminal()
       	{
       	  UI = G4UImanager::GetUIpointer();
       	  UI->SetCoutDestination(this);
       	  //  ...
       	}

   Similarly, `UI->SetCoutDestination(NULL)` must be added to the destructor of the class.

3. Write or modify the main program. To modify `exampleN01` to produce a log file, derive a class as described in step 1 above, and add the following lines to the main program:

       	#include "MySession.hh"
       	main()
               {
       	  // get the pointer to the User Interface manager
       	  G4UImanager* UI = G4UImanager::GetUIpointer();
       	  // construct a session which receives G4cout/G4cerr
       	  MySession * LoggedSession = new MySession;
       	  UI->SetCoutDestination(LoggedSession);
       	  // session->SessionStart(); // not required in this case
                 // .... do simulation here ...

       	  delete LoggedSession;
       	  return 0;
       	}

Note: | G4cout/G4cerr should not be used in the constructor of a class if the instance of the class is intended to be used as `static`. This restriction comes from the language specification of C++. See the documents below for details.

M.A.Ellis, B.Stroustrup. ``Annotated C++ Reference Manual'', Section 3.4
P.J.Plauger, ``The Draft Standard C++ Library''

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