Gfortran and Undefined reference to '__[module_name]_MOD_[function_name]'

i am writing a program in Fortran which uses .mod files, .dll libraries and .h headers.

I must be forgetting something when i call the compiler, because i get the error: undefined reference to '__[module_name]_MOD_[function_name]', where [module_name] is the name of one of the modules used by the main program and [function_name] is the name of a function contained in the module.

The only source file is called MAIN.f90:

! WORHP workspace access macros
#include "worhp/macros.h"

MODULE WORHP_INTERFACE

  USE std
  USE problem_definition_tools

CONTAINS

  SUBROUTINE OBJ(N,X,F) BIND(C)
    INTEGER(WORHP_INT)  :: N
    REAL(WORHP_DOUBLE)  :: X(N),F
    INTENT(in)          :: N, X
    INTENT(out)         :: F
    F = X(1)
  END SUBROUTINE OBJ

  SUBROUTINE CON(N,M,X,G) BIND(C)
    INTEGER(WORHP_INT)  :: N,M
    REAL(WORHP_DOUBLE)  :: X(N),G(M)
    INTENT(in)          :: N, M, X
    INTENT(out)         :: G
    TYPE (orbit)        :: O
    O = final_orbit(X)
    G = [O%Lp, O%La]
  END SUBROUTINE CON

  SUBROUTINE DOBJ(N,dfnnz,DFROW,X,DF) BIND(C)
    INTEGER(WORHP_INT)  :: N,dfnnz,DFROW(DFnnz)
    REAL(WORHP_DOUBLE)  :: X(N),DF(DFnnz)
    INTENT(in)          :: N, DFnnz, DFrow, X
    INTENT(out)         :: DF
    DF = [1, 0, 0, 0, 0, 0]
  END SUBROUTINE DOBJ

  SUBROUTINE DCON(N,M,DGnnz,DGROW,DGCOL,X,DG) BIND(C)
    INTEGER(WORHP_INT)  :: N,M,DGnnz,DGROW(DGnnz),DGCOL(DGnnz)
    REAL(WORHP_DOUBLE)  :: X(N),DG(DGnnz)
    INTENT(in)          :: N,M,DGnnz,DGrow,DGcol,X
    INTENT(out)         :: DG
    ! Dummy
  END SUBROUTINE DCON

  SUBROUTINE HESS(N,M,HMnnz,HMrow,HMcol,X,Mu,HM) BIND(C)
    INTEGER(WORHP_INT)  :: N, M, HMnnz, HMrow(HMnnz), HMcol(HMnnz)
    REAL(WORHP_DOUBLE)  :: X(N),Mu(M),HM(HMnnz)
    INTENT(in)          :: N, M, HMnnz, HMrow, HMcol, X, Mu
    INTENT(out)         :: HM
    ! Dummy
  END SUBROUTINE HESS

END MODULE WORHP_INTERFACE

program MAIN

  USE WORHP_INTERFACE
  USE Worhp_User

  INTEGER (WORHP_INT) :: Mode, N, M, DFnnz, DGnnz, HMnnz
  PARAMETER (N=6, M=2, DFnnz=1, DGnnz=12, HMnnz=12)
  INTEGER (WORHP_INT) :: DFrow(DFnnz), DGrow(DGnnz), DGcol(DGnnz)
  INTEGER (WORHP_INT) :: HMrow(HMnnz), HMcol(HMnnz)
  INTEGER (WORHP_INT) :: Iparam(10)
  REAL (WORHP_DOUBLE) :: X(N), L(N+M), U(N+M), Dparam(10)
  REAL (WORHP_DOUBLE) :: Infty = 1d20

  ! Check Version of library and header files
  CHECK_WORHP_VERSION

  L = [9000.0, 0.0, 0.0, 0.0, 0.0, 0.0, 200000.0, 35786000.0]
  U = [10000.0, 5.0, 180.0, 0.15, 180.0, 0.15, 200000.0, 35786000.0]

  X = [9520.00, 1.47490136, 71.50755639, 0.09948622, 97.00248532, 0.09296147]

  DFrow = [6]
  DGrow = [1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2]
  DGcol = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6]
  HMrow = [1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2]
  HMcol = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6]

  ! Get default parameter values
  Mode = 0

  CALL WorhpSimple(Mode, N, M, X, L, U, Dparam, Iparam, &
       DFnnz, DFrow, DGnnz, DGrow, DGcol, HMnnz, HMrow, HMcol, &
       OBJ, CON, DOBJ, DCON, HESS)

  ! User-defined derivatives are available
  Iparam(1) = 1
  Iparam(2) = 0
  Iparam(3) = 0

  ! Run the solver
  Mode = 1

  CALL WorhpSimple(Mode, N, M, X, L, U, Dparam, Iparam, &
       DFnnz, DFrow, DGnnz, DGrow, DGcol, HMnnz, HMrow, HMcol, &
       OBJ, CON, DOBJ, DCON, HESS)

end

The function final_orbit called by the subroutine CON is contained in the module "problem_definition_tools".

For the compilation i use the following windows batch file called "compile.bat"

x86_64-w64-mingw32-gfortran src\MAIN.f90 -cpp -Iinclude -Ifinclude\worhp -Ifinclude\aerospace -Jobj -Lbin -lworhp -o bin\megaceppa.exe

which gives the error

undefined reference to '__problem_definition_tools_MOD_final_orbit'

I run the command from the directory 'Test' which has the following structure

• \bin\
  • libworhp.dll
• \finclude
  • \worhp\
    • std.mod
  • \aerospace\
    • problem_definition_tools.mod
• \include
  • \worhp\
    • macros.h
• \lib
  • libworhp.lib
• \obj
  • worhp_interface.mod
• \src
  • MAIN.f90
• compile.bat

I would like to specify that the module "problem_definition_tools" is written by me, and i know for sure that it works because i already used it in another program. Moreover, i re-compiled it with x86_64-w64-mingw32-gfortran in order to avoid any compatibility issues with this program.

I am sure that there is something wrong in the way i call the compiler, but i can't figure it out because of my limited experience with Fortran. I also triend to search for similar questions on this website, but i couldn't find anything closely related to my problem.