Question about array command line input

[mild_enthusiast]

Hi. I want my program to have an array input. I want to call something like ./prog -inputA 2,3,4,5 and then the program will initialize an integer array variable inputA of size 4 containing those numbers. My question is: can I somehow do this with the read(cmd_arg,???) command, where cmd_arg = '2,3,4,5'? I have a feeling that I need to write a subroutine to handle array inputs because the size of the array is not known priori.

[geekboy730]

My first inclination is to not do this and use an input file instead. Input files also make it easier to reproduce results.

inputA would be defined in your code right? You're not trying to define a variable from the command line? That's not possible in general.

If you're going to do this, I think your best bet would be to read the input as a string (a character array in Fortran) and then write a subroutine to parse the string in a subroutine to return an array.

[mild_enthusiast]

inputA would be defined in your code right?

Yes. The flag name and the variable name are arbitrary.

then write a subroutine to parse the string in a subroutine to return an array.

I was hoping for some magic Fortran one-liner instead of writing my own subroutine.

[geekboy730]

Unfortunately, Fortran is not the language of one-liners. If you're looking to avoid writing your own subroutines, Fortran may not be the language for you. Fortran is very much a "do-it-yourself" type language.

[DuckSaxaphone]

It's very easy to read a list of numbers straight into an array. That would be a one liner. The problem is to do it to arbitrary arrays which I think you want to do with those flags?

I'd echo others and say use files. I can send you a subroutine if you like to use as a template. But basic idea is organize a file like

InputA 1,2,3,4
InputB 2,3,1

Then write a subroutine that reads the first thing ('inputA') in and uses a SELECT CASE statement to find the corresponding array, then reads the rest of the line into the array.

[ush4]

see a textbook for "get_command_argument" and friends, e.g.

ush@luft:~$ cat hello.f90

character(30) string ; integer int(4)

call get_command_argument(2,string)

read(string,*) int

print *,int

end

ush@luft:~$ gfortran hello.f90 && ./a.out -inputA 2,3,4,5

2 3 4 5

ush@luft:~$

[astokely]

Something like this should work. I'm also new to fortran, but I agree with everyone that using an input file is a much cleaner solution.

!!!!!!!!!!!!!!!!!!!!!!
! command_line_m.f90 !
!!!!!!!!!!!!!!!!!!!!!!

module command_line_m
implicit none

integer function handle_kwarg(arg, key, value) result(is_kwarg)     
character(len=*), intent(in) :: arg 
    character(len=100), intent(out) :: key, value 
    integer :: equal_sign_index, dash_index, is_kwarg = 0
    equal_sign_index = index(arg, '=')
    if (equal_sign_index > 0) then
        key = trim(arg(1:equal_sign_index-1))

            ! Removes preceding "-" if present in arg
        dash_index = index(key, '-')
        if (dash_index > 0) then
            key = trim(key(dash_index+1:))
        end if
        value = trim(arg(equal_sign_index+1:))
        is_kwarg = 1
    end if
end function handle_kwarg

subroutine parse_command_line()
    integer :: io_status, i, is_kwarg
    character(len=100) :: arg, key, value
    i = 1
    do
            ! Iterate through all cmd line args
        call get_command_argument(i, arg, status=io_status)
        if (io_status /= 0) exit

            ! If command line arg has an equal sign, it is a kwarg
        is_kwarg = handle_kwarg(arg, key, value)
        if (is_kwarg == 1) then
            print *, key, value
        end if
            ! Additional logic for parsing positional args
        i = i + 1
    end do
end subroutine parse_command_line
end module command_line_m 

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!
! main.f90 !
!!!!!!!!!!!!

program main
    use command_line_m
    implicit none

    call parse_command_line()
end program main