Writing characters in OpenACC subroutines

Characters are an aggregate variable according to the OpenACC specification

OpenACC 3.3 Glossary 6

Aggregate variables – a variable of any non-scalar datatype, including array or composite variables.
In Fortran, this includes any variable with allocatable or pointer attribute and character variables.

Writing while in a device subroutine is not covered in OpenACC. However, there are differences between the compilers, we tested everything with the following program

Code

program main
  implicit none
  character(len=12) :: message = "Success"
  write(*,*) "Checking if characters can be printed in acc nohost subroutine ..."
  call write_message(message)

contains
  subroutine write_message(message)
    !$acc routine seq
    implicit none
    character(len=12), intent(in) :: message
    character(len=14) :: new_message
    new_message = message(1:7) // "!"
    write(*,*)new_message
  end subroutine
end program

Compiler behaviour

Compiler	Result	Correctness	Notes
Cray Fortran 19.0.0	❌ Compile error	Not covered by spec	Characters are not supported at all in device subroutines; the ftn-7066 error is shown below.
nvfortran 25.3-0	✅ OK	Not covered by spec	Compiles, runs and prints the message.

The Cray compile error:

Code

    new_message = message(1:7) // "!"
ftn-7066 ftn: ERROR WRITE_MESSAGE, File = characters_cray.f90, Line = 13
  Unsupported accelerator code error: Fortran character

    write(*,*)new_message
ftn-7066 ftn: ERROR WRITE_MESSAGE, File = characters_cray.f90, Line = 14
  Unsupported accelerator code error: Fortran character -- new_message