GFortran and CodeBlocks issue with Modules and Multiple Files - fortran

Question

I am working with GFortran and CodeBlocks but I'm having an issue about Modules and Multiple files.
i keep getting this error:
Fatal Error: Can't open module file 'mesh.mod' for reading at (1): No such file or directory
For some reason, GFortran is not building the 'mesh.mod' file.
This problem does not occur when I put all the code in a single .f90 file.
Bellow is an example of code that this error happens.
main.f90
MODULE MESH
IMPLICIT NONE
INTEGER :: IMAX,JMAX,NMAX
REAL(8), ALLOCATABLE :: XD(:),YD(:),FX(:,:),FY(:,:)
REAL(8) :: PI,E,DX,DY,H,L,RHO,MU
PARAMETER (PI = ACOS(-1.D0))
PARAMETER (E = 2.718)
END MODULE MESH
!**************************************************************
program Cavity
Use Mesh
implicit none
Real(8), Allocatable :: func(:)
Real(8) :: Der,DfDx
integer :: i
IMAX=10
DX=1./10
Allocate(xd(IMAX),func(IMAX))
Do i=1,IMAX
xd(i)=i*DX
End Do
Do i=1,IMAX
func(i) = xd(i)**2
End Do
Der=Dfdx(func,2)
Write(*,*) Der
End program Cavity
Derivatives.f90
Real(8) Function DfDx(f,i)
Use Mesh
implicit none
Real(8) :: f(1:Imax)
integer :: i
DfDx=(f(i+1)-f(i-1))/(2d0*dx)
return
end function DfDx
When I use console command line compilation instead of CodeBlocks interface I already solved this problem (Compiling Multiple Files with modules) but I'm still getting this problem with CodeBlocks.
Does anyone know how to solve this issue?

Answer 1

Assuming what you have written is how your code is, then it appears that the problem is that the module mesh is inside the main program and not a separate file. You should have three files: Mesh.f90, Derivatives.f90 and Main.f90.
Mesh.f90 is exactly as you have it,
module Mesh
implicit none
integer :: IMAX,JMAX,NMAX
real(8), allocatable :: XD(:),YD(:),FX(:,:),FY(:,:)
real(8) :: PI,E,DX,DY,H,L,RHO,MU
parameter (PI = ACOS(-1.D0))
parameter (E = 2.718)
end module Mesh
Derivatives.f90 should be written as another module, using contains:
module Derivatives
use mesh
contains
real(8) function dfdx(f,i)
real(8) :: f(i:imax)
integer :: i
DfDx=(f(i+1)-f(i-1))/(2d0*dx)
end function dfdx
end module Derivatives
and the Main.f90 will then use both modules. Note that I had to eliminate the variable DfDx; this is because it conflicts with the function DfDx in module Derivatives
program Cavity
Use Mesh
use Derivatives
implicit none
Real(8), Allocatable :: func(:)
Real(8) :: Der
integer :: i
IMAX=10
DX=1./10
Allocate(xd(IMAX),func(IMAX))
Do i=1,IMAX
xd(i)=i*DX
End Do
Do i=1,IMAX
func(i) = xd(i)**2
End Do
Der=Dfdx(func,2)
Write(*,*) Der
End program Cavity
I do not know how CodeBlocks works, but I would presume it lets you choose the compilation order. If that is the case, you should compile Mesh.f90 first, then Derivatives.f90, then compile Main.f90 before linking them to an executable.
When I compiled & linked them, I got an answer of 0.200000002980232; hopefully that links up to what you have as well.

Answer 2

On codeblock, you may go to Project properties > Build targets
Then select the file you want to build first (say mod.f90).
In the "Selected file properties" go to "Build"
Here,change the priority weight. Lower weight implies the file will be built first.

Answer 3

The problem is that in CodeBlocks "projects are built in the order of appearence, from top to bottom" (CodeBlocks Wiki), in other words, the files are compiled alphabetically.
Which means that in my case, Derivatives.f90 was being compiled before than Main.f90 causing the error.
A way to circumvent the problem is to set only the Main.f90 file as build target in CodeBlocks:
Menu Project/Properties...
In Build Target Files at the tab Build targets check only Main.f90
And use the command Include 'File_Name.f90' inside the Main.f90 code to include the other f90 files for compilation in the right order.