I want to wrap the fortran write-statement in a custom subroutine or function which includes some additional debug-logic.
But I'm currently stuck with defining the prototype of the function/subroutine. Is this possible? If yes, how?
3
votes
are you trying to modify the behavior of the write statement without modifying the write statement syntax by wrapping it in your own function call? Short answer you cant do that. Maybe some preprocessor tricks will get you there but i think it would be a mess.
– agentp
Ah, that sounds not good. I simply wanted to put a short-circuit in front of the write (if (flag .neqv. .true.) then return end if) to globally control if output happens or not. Beside that, the function should simply delegate to write.
– Joachim Rosskopf
3 Answers
3
votes
The title of your question exhibits a misunderstanding, though the text suggests you know better. Nevertheless, for the record, write is a Fortran statement, it is neither a subroutine nor a function.
I think you have a number of options. One, which I have used occasionally, would be to write a function which returns a string. Perhaps
function error_message(error)
character(len=*), intent(in) :: error
character(len=:), allocatable :: error_message
error_message = 'ERROR: '//trim(error)
end function error_message
which you can then use like this
write(*,*) error_message('Oh s**t')
You could certainly write a subroutine or a function with side effects which include writing to an ouput channel, but if you adopt this approach you have to be careful to observe the rules for recursive i/o.
EDIT
after OP's comment.
If you want to switch off debug messages another option you have is to direct them to a null device or file, eg /dev/null on Linux or NUL on Windows. Something like
integer, parameter :: debug_channel = 99
logical, parameter :: debugging = .false.
...
if (debugging) then
open(debug_channel, file='NUL')
else
open(debug_channel, file='debuglog'
end if
and then
write(debug_channel,*) 'message'
2
votes
a relatively simple way to accomplish most of what you want is to simply put the if inline in front of every write that is subject to debug control:
if(debug)write(..,..)..
where debug is a global logical value, or even:
if(debugf(level))write(..,..)..
where the logical function debugf determines whether to write based on some argument.
1
votes
In addition to the other answers, you may be able to avoid using if (debug) write... with derived type IO.
I say "may", as it is quite silly unless you already have a suitable structure, and compiler support is currently rare.
However, as an example, compiled with ifort 14.0.1:
module errormod
type error_t
character(len=:), allocatable :: message
contains
procedure write_error
generic :: write(formatted) => write_error
end type error_t
logical debug_verbose
contains
subroutine write_error(err, unit, iotype, v_list, iostat, iomsg)
class(error_t), intent(in) :: err
integer, intent(in) :: unit
character(len=*), intent(in) :: iotype
integer, intent(in), dimension(:) :: v_list
integer, intent(out) :: iostat
character(len=*), intent(inout) :: iomsg
if (debug_verbose) then
write(unit, '("Error: ", A)', iostat=iostat, iomsg=iomsg) err%message
else
write(unit, '()', advance='no')
end if
end subroutine write_error
end module errormod
program test
use errormod
implicit none
type(error_t) error
debug_verbose = .TRUE.
error%message = "This error will be reported."
write(*, '(dt)') error
debug_verbose = .FALSE.
error%message = "This error will not be reported."
write(*, '(dt)') error
debug_verbose = .TRUE.
error%message = "This final error will also be reported."
write(*, '(dt)') error
end program test
The first and third messages will appear, but not the second.
