I am experiencing an allocation failure when using allocatable character strings as optional arguments. The problem only occurs when I call through two levels of procedures. In my actual code call get_level1() (see below) represents a call to a list data structure and call get_level2() represents the list calling the same type of accessor function on one of its records. I have stripped down an example to the bare minimum that adequately reproduces the problem.
In the code below when I call get_level2 directly the expected character string is returned through the optional argument. When I call get_level1 which in turn calls get_level2 allocation of the optional dummy argument fails. Using gdb I find the allocation attempt to create a character*1635... when it gets back to the actual argument is obviously has an integer overflow because it thinks the allocation is character*-283635612...
My actual code has many optional arguments not just one. As a simple example I added an optional integer argument. This time instead of a segmentation fault I get a null string.
In the second example the integer argument works regardless of using the character argument. (I would expect this since no dynamic allocation is being performed) The integer's presence has no effect on the character. I have also tried changing the intent to (inout). This does not change the behavior, though I did not expect it to. [I believe that intent(out) causes the actual argument to deallocate first, and intent(inout) retains the actual argument's allocation state]
call get_level1( NUM=n ) ! works
call get_level1( NUM=n, TEXT=words ) ! fails
call get_level1( TEXT=words ) ! fails
my compile cmd is:
gfortran -Wall -g -std=f2008ts stest1.f08 -o stest
Environment
Linux 4.15.0-42-generic #45-Ubuntu SMP x86_64 GNU/Linux
GNU Fortran (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0
Example with one optional argument
module stest1
implicit none
character(:), allocatable :: data
contains
subroutine get_level2( TEXT )
implicit none
character(:), optional, allocatable, intent(out) :: TEXT
if ( PRESENT( TEXT ) ) then
TEXT = 'Prefix: ' // data // ' :postfix'
end if
end subroutine get_level2
subroutine get_level1( TEXT )
implicit none
character(:), optional, allocatable, intent(out) :: TEXT
call get_level2( TEXT )
end subroutine get_level1
end module stest1
program main
use stest1
implicit none
character(:), allocatable :: words
data = 'Hello Doctor'
call get_level1( words )
write(*,100) words
100 format( 'words = [',A,']' )
end program main
Example with two optional arguments
module stest2
implicit none
character(:), allocatable :: data
integer :: count
contains
subroutine get_level2( TEXT, NUM )
implicit none
character(:), optional, allocatable, intent(out) :: TEXT
integer, optional, intent(out) :: NUM
if ( PRESENT( TEXT ) ) then
TEXT = 'Prefix: ' // data // ' :postfix'
end if
if ( PRESENT( NUM ) ) then
NUM = count
end if
end subroutine get_level2
subroutine get_level1( TEXT, NUM )
implicit none
character(:), optional, allocatable, intent(out) :: TEXT
integer, optional, intent(out) :: NUM
call get_level2( NUM=NUM, TEXT=TEXT )
end subroutine get_level1
end module stest2
program main
use stest2
implicit none
character(:), allocatable :: words
integer :: n
count = 42
data = 'Hello Doctor'
call get_level1( TEXT=words )
write(*,100) words
write(*,110) n
100 format( 'words = [',A,']' )
110 format( 'N = [',I0,']' )
end program main
