c++ - 什么时候调用删除操作符？

Question

下面的代码重复使用了 new 关键字。我在 stackoverflow 上读到应该有一个相应的调用 delete每次调用 new。代码取自Geant4。我的问题是每次调用 new 是否都应该在这段代码中调用 delete ？

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B1DetectorConstruction::B1DetectorConstruction()
: G4VUserDetectorConstruction(),
  fScoringVolume(0)
{ }

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B1DetectorConstruction::~B1DetectorConstruction()
{ }

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G4VPhysicalVolume* B1DetectorConstruction::Construct()
{  
  // Get nist material manager
  G4NistManager* nist = G4NistManager::Instance();

  // Envelope parameters
  //
  G4double env_sizeXY = 20*cm, env_sizeZ = 30*cm;
  G4Material* env_mat = nist->FindOrBuildMaterial("G4_WATER");

  // Option to switch on/off checking of volumes overlaps
  //
  G4bool checkOverlaps = true;

  //     
  // World
  //
  G4double world_sizeXY = 1.2*env_sizeXY;
  G4double world_sizeZ  = 1.2*env_sizeZ;
  G4Material* world_mat = nist->FindOrBuildMaterial("G4_AIR");

  G4Box* solidWorld =    
    new G4Box("World",                       //its name
       0.5*world_sizeXY, 0.5*world_sizeXY, 0.5*world_sizeZ);     //its size

  G4LogicalVolume* logicWorld =                         
    new G4LogicalVolume(solidWorld,          //its solid
                        world_mat,           //its material
                        "World");            //its name

  G4VPhysicalVolume* physWorld = 
    new G4PVPlacement(0,                     //no rotation
                      G4ThreeVector(),       //at (0,0,0)
                      logicWorld,            //its logical volume
                      "World",               //its name
                      0,                     //its mother  volume
                      false,                 //no boolean operation
                      0,                     //copy number
                      checkOverlaps);        //overlaps checking

  //     
  // Envelope
  //  
  G4Box* solidEnv =    
    new G4Box("Envelope",                    //its name
        0.5*env_sizeXY, 0.5*env_sizeXY, 0.5*env_sizeZ); //its size

  G4LogicalVolume* logicEnv =                         
    new G4LogicalVolume(solidEnv,            //its solid
                        env_mat,             //its material
                        "Envelope");         //its name

  new G4PVPlacement(0,                       //no rotation
                    G4ThreeVector(),         //at (0,0,0)
                    logicEnv,                //its logical volume
                    "Envelope",              //its name
                    logicWorld,              //its mother  volume
                    false,                   //no boolean operation
                    0,                       //copy number
                    checkOverlaps);          //overlaps checking

  //     
  // Shape 1
  //  
  G4Material* shape1_mat = nist->FindOrBuildMaterial("G4_A-150_TISSUE");
  G4ThreeVector pos1 = G4ThreeVector(0, 2*cm, -7*cm);

  // Conical section shape       
  G4double shape1_rmina =  0.*cm, shape1_rmaxa = 2.*cm;
  G4double shape1_rminb =  0.*cm, shape1_rmaxb = 4.*cm;
  G4double shape1_hz = 3.*cm;
  G4double shape1_phimin = 0.*deg, shape1_phimax = 360.*deg;
  G4Cons* solidShape1 =    
    new G4Cons("Shape1", 
    shape1_rmina, shape1_rmaxa, shape1_rminb, shape1_rmaxb, shape1_hz,
    shape1_phimin, shape1_phimax);

  G4LogicalVolume* logicShape1 =                         
    new G4LogicalVolume(solidShape1,         //its solid
                        shape1_mat,          //its material
                        "Shape1");           //its name

  new G4PVPlacement(0,                       //no rotation
                    pos1,                    //at position
                    logicShape1,             //its logical volume
                    "Shape1",                //its name
                    logicEnv,                //its mother  volume
                    false,                   //no boolean operation
                    0,                       //copy number
                    checkOverlaps);          //overlaps checking

  //     
  // Shape 2
  //
  G4Material* shape2_mat = nist->FindOrBuildMaterial("G4_BONE_COMPACT_ICRU");
  G4ThreeVector pos2 = G4ThreeVector(0, -1*cm, 7*cm);

  // Trapezoid shape       
  G4double shape2_dxa = 12*cm, shape2_dxb = 12*cm;
  G4double shape2_dya = 10*cm, shape2_dyb = 16*cm;
  G4double shape2_dz  = 6*cm;      
  G4Trd* solidShape2 =    
    new G4Trd("Shape2",                      //its name
              0.5*shape2_dxa, 0.5*shape2_dxb, 
              0.5*shape2_dya, 0.5*shape2_dyb, 0.5*shape2_dz); //its size

  G4LogicalVolume* logicShape2 =                         
    new G4LogicalVolume(solidShape2,         //its solid
                        shape2_mat,          //its material
                        "Shape2");           //its name

  new G4PVPlacement(0,                       //no rotation
                    pos2,                    //at position
                    logicShape2,             //its logical volume
                    "Shape2",                //its name
                    logicEnv,                //its mother  volume
                    false,                   //no boolean operation
                    0,                       //copy number
                    checkOverlaps);          //overlaps checking

  // Set Shape2 as scoring volume
  //
  fScoringVolume = logicShape2;

  //
  //always return the physical World
  //
  return physWorld;
}

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Answer 1

查看论坛和manual我找到了

Any physical volume must be allocated using 'new' in the user's program; they get registered to a G4PhysicalVolumeStore at construction, which will also take care to deallocate them at the end of the job, if not done already in the user's code.

在 Geant4 论坛中也有讨论 here