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 Whosebug 上读到，每次调用 new 都应该对应调用 delete。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 我发现

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.

Geant4论坛也有讨论here

什么时候调用删除操作符？

When to call the delete operator?

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