CODEWITHSUNDEEP
modulefortran
northernaland
northernaland

Reputation: 27

How to use a module which includes another module in Fortran?

I want to do something like this:

main.f90 uses module A and module B.
module_A.f90 is independent.
module_B.f90 uses module A.

My code is like this:

main.f90

include "module_A.f90"
include "module_B.f90"

program MAIN
use A
use B
write(*,*) Array(I)

end program MAIN

module_A.f90

module A

integer, parameter :: I = 10

end

module_B.f90

include "module_A.f90"

module B

use A

real*8 :: Array(I)=1d0

end module B

However, the error information shows:

Error: module_A name 'module_A' at (1) is already being used as a MODULE at (2)

It seems that I can't use a module to cite another module. Is there any way to solve this problem?

(Note: it is not the problem of missing "contains" because it doesn't involve subroutine or function)

Upvotes: 1

Views: 2780

Answers (1)

PTRK
PTRK

Reputation: 929

The problem

when you included modA.f90 and modB.f90 in main.f90, since you already included modA.90 in modB.90, then your main.f90 look like this:

module modA
...
end module

module modA
...
end module

module modB
use mod A
...
end module

program 

...
end program

Since in fortran you can't have two unitwith the same name, the compiler fails with the error you see because you declared two module modA.

Fixing with use statement (recommended)

modA.f90

module modA.f90
...
end module

modB.90

module modB
use modA
...
end module

main.f90

program main
use modB
use modA
...
end program

However usestatement needs to deals with dependencies, so modA.90 must be compiled before modB.f90

gfortran -o main modA.f90 modB.90 main.f90

Fixing with include statement (depreciated)

I do not recommend this solution, but for the sake of completness, it is provided.

First answer

modA.f90

module modA.f90
...
end module

modB.90

module modB
use modA
...
end module

main.f90

include modA.f90
include modB.f90

program main

use modB
use modA
...
end program

In this case, since include is like copy-pasting, we only need to compile the program

gfortran -o main main.f90

Second answer

modA.f90

module modA.f90
...
end module

modB.90

include modA.f90

module modB
use modA
...
end module

Since modA is already included, no need to do it again

main.f90

include modB.f90

program main

use modB
use modA
...
end program

Again we only need to compile the program

gfortran -o main main.f90

Upvotes: 3

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