Deallocate pointer in fortran [duplicate] - pointers

Question

My IDE is Code::Blocks 17.2 with compiler GFortran 6.3.1
The all code is:
PROGRAM EES_TEST
USE , NON_INTRINSIC :: DERIVED_TYPE
IMPLICIT NONE
INTEGER :: I , ALLOC_ERR , DEALLOC_ERR
LOGICAL :: GLOBAL_ERR
CLASS ( TRONA ) , POINTER :: P_TRA
TYPE ( TRONA ) , ALLOCATABLE , TARGET :: TRAN(:)
IF ( .NOT. ALLOCATED ( TRAN ) ) ALLOCATE ( TRAN ( 2 ) , STAT = ALLOC_ERR )
IF ( ALLOC_ERR .NE. 0 ) STOP ("PROBLEM WITH MEMORY ALLOCATION - TRAN!!!")
OPEN ( UNIT = 15 , FILE = 'INPUT.TXT' , ACTION = 'READ' )
DO I = 1 , 2
P_TRA => TRAN ( I )
GLOBAL_ERR = P_TRA%UCI()
IF ( GLOBAL_ERR .EQV. .TRUE. ) STOP ("ERROR WITH READING FROM OUTPUT.TXT!")
END DO
CLOSE ( 15 )
IF ( ALLOCATED ( TRAN ) ) DEALLOCATE ( TRAN , STAT = DEALLOC_ERR )
IF ( DEALLOC_ERR .NE. 0 ) STOP ("PROBLEM WITH MEMORY DEALLOCATION - TRAN!!!")
END PROGRAM EES_TEST
MODULE DERIVED_TYPE
IMPLICIT NONE
TYPE , PUBLIC :: TRONA
PRIVATE
REAL :: Sn
REAL :: Vn
CONTAINS
PROCEDURE , PUBLIC :: UCI => UCI_POD_TRONA
PROCEDURE , PUBLIC :: TAKE_Sn => TAKE_POD_Sn
PROCEDURE , PUBLIC :: TAKE_Vn => TAKE_POD_Vn
END TYPE TRONA
PRIVATE :: UCI_POD_TRONA
PRIVATE :: TAKE_POD_Sn , TAKE_POD_Vn
CONTAINS
FUNCTION UCI_POD_TRONA ( THIS ) RESULT ( WRONG )
IMPLICIT NONE
CLASS ( TRONA ) :: THIS
LOGICAL :: WRONG
WRONG = .FALSE.
READ ( 15 , * , ERR = 100 ) THIS%Sn
READ ( 15 , * , ERR = 101 ) THIS%Vn
RETURN
100 WRITE (*,*) "WRONG FORMAT - INPUT 100!"
WRONG = .TRUE.
STOP
101 WRITE (*,*) "WRONG FORMAT - INPUT 101!"
WRONG = .TRUE.
STOP
END FUNCTION UCI_POD_TRONA
FUNCTION TAKE_POD_Sn ( THIS ) RESULT ( POD_Sn )
IMPLICIT NONE
CLASS ( TRONA ) :: THIS
REAL :: POD_Sn
POD_Sn = THIS%Sn
RETURN
END FUNCTION TAKE_POD_Sn
FUNCTION TAKE_POD_Vn ( THIS ) RESULT ( POD_Vn )
IMPLICIT NONE
CLASS ( TRONA ) :: THIS
REAL :: POD_Vn
POD_Vn = THIS%Vn
RETURN
END FUNCTION TAKE_POD_Vn
END MODULE DERIVED_TYPE
I am very new in object oriented programing in Fortran so I need an explanation about using the object pointer for calling methods from derived types. In this case I want to check is there any problem with memory leaking and if it is case is there method for checking how much memory was lost and in which line? Another thing is nullifying the derived type pointer. How to do that for this case?

Answer 1

Generally, unless you allocate something somewhere, you cannot have memory leaks. It is simply impossible. You can only leak something you allocate as a pointer target, nothing else.
In your code you have no allocate() for a pointer, so there cannot be any memory leaks.
For a memory leak to happen, two things must happen in sequence.
An anonymous pointer target must be allocated. That is possible only through the allocate statement
allocate(p_tra)
The pointer to the target is lost. Either it is redirected somewhere else
p_tra => somewhere_else
Or it ceases to exist, because it is a local variable of a subroutine that finishes or it is a component of a structure which is deallocated or similar...
You can always use GCC sanitizations -fssnitize=leak or valgrind to check for memory leaks.
Regarding the nulifying, just use the nulify statement or assign to null(). It is a pointer like any other.
p_tra => null()