main.F90
program main
use my_module
real(8) :: a, b
a = 1.3
b = 2.4
call my_subroutine1(a)
!call my_subroutine2(a)
end program main
test.F90
module my_module
contains
subroutine my_subroutine1(a, b)
class(*), intent(in) :: a
class(*), intent(in), optional :: b
select type (a)
type is (real(4))
print*, 'real 4 a (my_subroutine1): ', a
type is (real(8))
print*, 'real 8 a (my_subroutine1): ', a
end select
if (present(b)) then
print*, 'b is present in subroutine1'
select type (b)
type is (real(4))
print*, 'real 4 b: ', b
type is (real(8))
print*, 'real 8 b: ', b
end select
else
end if
call my_subroutine3(a, b)
end subroutine my_subroutine1
subroutine my_subroutine2(a, b)
real(8), intent(in) :: a
real(8), intent(in), optional :: b
print*, 'real 8 a (my_subroutine2): ', a
if (present(b)) then
print*, 'b is present in subroutine2'
print*, 'real 8 b: ', b
else
end if
call my_subroutine3(a, b)
end subroutine my_subroutine2
subroutine my_subroutine3(a, b)
class(*), intent(in) :: a
class(*), intent(in), optional :: b
select type (a)
type is (real(4))
print*, 'real 4 a (my_subroutine3): ', a
type is (real(8))
print*, 'real 8 a (my_subroutine3): ', a
end select
if (present(b)) then
print*, 'b is present in subroutine3'
select type (b)
type is (real(4))
print*, 'real 4 b: ', b
type is (real(8))
print*, 'real 8 b: ', b
end select
end if
end subroutine my_subroutine3
end module my_module
When main calls my_subroutine1(a), output is
real 8 a (my_subroutine1): 1.29999995231628
real 8 a (my_subroutine3): 1.29999995231628
However, when main calls my_subroutine2(a), output is
real 8 a (my_subroutine2): 1.29999995231628
real 8 a (my_subroutine3): 1.29999995231628
b is present in subroutine3
forrtl: severe (408): fort: (7): Attempt to use pointer B when it is not associated with a target
Image PC Routine Line Source
a.out 00000000004072A0 Unknown Unknown Unknown
a.out 0000000000404897 my_module_mp_my_s 62 test.F90
a.out 0000000000403CA2 my_module_mp_my_s 41 test.F90
a.out 0000000000404984 MAIN__ 10 main.F90
a.out 0000000000402B9E Unknown Unknown Unknown
libc-2.17.so 00007F05EDED2555 __libc_start_main Unknown Unknown
a.out 0000000000402AA9 Unknown Unknown Unknown
In the second case (calling my_subroutine2), why does my_subroutine3 think the optional argument is present?
I understand that I can do something like this in my_subroutine2
if (present(b)) then
call my_subroutine3(a,b)
else
call my_subroutine3(a)
end if
but with all b's being an optional dummy argument in all 3 subroutines, this is not required as supported by my_subroutine1.
Is using class(*) variable as optional dummy argument causing this problem? If that's the case, why does main calling my_subroutine1 work without an error?
