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I am attempting to link to a c++ subroutine package from a Fortran project but continue to get
error LNK2019: unresolved external symbol _mcea referenced in function _DOWUNRUN
my C++package looks like
extern "C" //prevent function name from being mangled
#include "rayopt.h"
double seed,oldrand[55];
int jrand;
extern "C" __declspec(dllexport)
//********************************************************************************************
void mcea(double seed, int no_solutions, double prob_crossover, double prob_mutation, double distribution_index_crossover,
double distribution_index_mutation, int no_objectives, int no_constraints, int no_variables, double upp_bound[],
double low_bound[], int type_variable[], double f77_parent_population[], double f77_parent_objective[],
double f77_parent_constraint[], int parent_type[], double f77_child_population[], double f77_child_objective[],
double f77_child_constraint[], int child_type[], int ii)
{
etc
and my fortran call looks like
Subroutine DoWunRun
Use, intrinsic :: ISO_C_Binding
Use Traj2dF_M
include "Traj2df.fi"
common/RWO/ig,Kruns
integer i,j,k,ig,Kruns,Mode
!
INTERFACE
Subroutine mcea(Seed,NumSol,ProbX,ProbM,DIX,DIM,
* NumObjs,NumConstr,NumVars,ovMaxLim,ovMinLim,type_variable,
* parent_population,parent_objective,parent_constraint,
* parent_type,child_population,child_objective,child_constraint,
* child_type,Mode) BIND(C,NAME="mcea")
Double Precision Seed
Integer NumSol
Double Precision ProbX,ProbM,DIX,DIM
Integer NumObjs,NumConstr,NumVars
Double Precision ovMaxLim(1),ovMinLim(*)
Double Precision parent_population(*),parent_objective(*)
Double Precision parent_constraint(*)
Double Precision child_population(*),child_objective(*)
Double Precision child_constraint(*)
Integer parent_type(*),child_type(*),type_variable(*)
Integer Mode
END
END INTERFACE
!
more code, then
Mode=0
call mcea(Seed,NumSol,ProbX,ProbM,DIX,DIM,
* NumObjs,NumConstr,NumVars,ovMaxLim,ovMinLim,type_variable,
* parent_population,parent_objective,parent_constraint,
* parent_type,child_population,child_objective,child_constraint,
* child_type,Mode)
!
etc
Whatever I try I still get the error.
Are there any Visual Studio settings I need to include?
Thanks in advance
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What version of Visual Fortran are you using? And, I assume you're building a 32-bit application?
--Lorri
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You don't say how the C++ library is specified in by the linker in the Fortran project. I see a dllexport in the C++ code, so are you building a DLL? If you made the C++ project a dependent of the Fortran project, expecting the library to be pulled in automatically, that doesn't work with C++ DLL projects due to a change Microsoft made some VS versions ago. In that case you will have to name the .lib explicitly in the Linker "Additional Dependencies" property or add the .lib to your Fortran project as if it were a source file. Do make sure that the runtime library types of the two projects match.
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I think Steve's suggestion will get you past the linking stage, but the C++ side is declaring all scalars to be passed by value while the Fortran interface is passing everything by reference. You need to fix this on the Fortran side by adding the declarations
Value Seed,NumSol,ProbX,ProbM,DIX,DIM Value NumObjs,NumConstr,NumVars,Mode
At the end of your declarations in the interface body for subroutine mcea. Also your interface body should contain IMPLICIT NONE because it can't inherit implicit typing from its host, not even through an IMPORT statement. Not to mention that it is my preference that the Fortran dummy argument names should match the names given on the C++ side, not only for clarity (the C++ documentation could then be read as the Fortran documentation) but when the Fortran compiler spits out an error about an actual argument to mcea you can compare more easily the C++ documentation and your Fortran subroutine call.

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