Re: Calling a function in C++ dll from FORTRAN

null@example.com (sankarnkp) — Wed, 04 Sep 2013 17:05:18 +0000

Jeff,

Using VALUE modifier worked in my case. There was one small issue in the C++ side, but the major fix for me was changing the modifier to VALUE. Thanks for your help.

Regards
Sankar

Re: Calling a function in C++ dll from FORTRAN

null@example.com (jeff) — Sun, 01 Sep 2013 14:38:56 +0000

In your interface, try using the VALUE modifier when declaring your parameters rather than INTENT(IN). I've had some better luck with that. Additionally, I noticed that your C declaration says to use the cdecl calling convention. This could theoretically be a problem (DLLs usually use the stdcall convention), but try using the VALUE modifier in your interface declarations first.

Calling a function in C++ dll from FORTRAN

null@example.com (sankarnkp) — Thu, 29 Aug 2013 18:08:40 +0000

Hi,
I am stuck at a point where I am using mixed language programming of C++ and FORTRAN. I have a C++ function in a dll which returns a pointer. I tried to call it from my FORTRAN program. I have no problem in compiling, linking and running. However, after the run I get the C pointer returned as 0. It is not a problem with the function in the dl because I have checked with the dll being called from both C++ and C# programs. So I think it is something to dow ith FORTRAN calling the C++ function. Here is the structure of the program:

// C++ Header
// ---------------
# include statements

#ifdef BUILD_DLL
#define DLL_EXPORT __declspec(dllexport)
#else
// #define DLL_EXPORT __declspec(dllimport)
#endif

//#ifdef __cplusplus
extern "C"
{

double DLL_EXPORT __cdecl *CalcAirProperties(int InputCombination, double Input1, double Input2, double Pressure);

}
// ---------------

//C++ source code
// ---------------

double DLL_EXPORT __cdecl *CalcAirProperties(int InputCombination, double Input1, double Input2, double Pressure)
{
double *AirProperties = new double[7];

//Do Calculations

return AirProperties

}

// ---------------

Here is my FORTRAN code:
!********************

PROGRAM ProgramMain

USE Statements
USE iso_c_binding, ONLY : c_ptr,c_double,c_f_pointer

IMPLICIT NONE

TYPE(c_ptr) :: c_p
REAL(c_double), POINTER :: f_p(:)

INTERFACE

FUNCTION CalcAirProperties(InputComb, InpValue1,InpValue2,BarometricPressure) BIND(C,NAME='CalcAirProperties')

USE ISO_C_BINDING

INTEGER(kind=C_INT), INTENT(IN) :: InputComb
REAL(kind=C_DOUBLE), INTENT(IN) :: InpValue1
REAL(kind=C_DOUBLE), INTENT(IN) :: InpValue2
REAL(kind=C_DOUBLE), INTENT(IN) :: BarometricPressure

TYPE(c_ptr) :: CalcAirProperties

END FUNCTION

END INTERFACE

REAL :: TempDB_Test
REAL :: TempRH_Test
REAL :: BaroPressure

TempDB_Test = 308.15
TempRH_Test = 0.69
BaroPressure = 101.325

c_p = CalcAirProperties(2,TempDB_Test,TempRH_Test,BaroPressure)

CALL c_f_pointer(c_p,f_p,[7])

RHiC = f_p(3)
RhoAiC = f_p(7)

END ProgramMain

!********************

In the above set up the pointer returned by the c_p=CalcAirProperties() call is 0 and thus the values f_p is not pointing to the right array start.

So to remove all the problems with pointers I converted the C++ function to accept an array (by reference) so that I can set the desired array values inside the C++ function and thus pass the array back to FORTRAN. Here is what I did for that:

// C++ Header
// ---------------
# include statements

#ifdef BUILD_DLL
#define DLL_EXPORT __declspec(dllexport)
#else
// #define DLL_EXPORT __declspec(dllimport)
#endif

//#ifdef __cplusplus
extern "C"
{

void DLL_EXPORT __cdecl CalcAirProperties(int InputCombination, double Input1, double Input2, double Pressure,double PropertyArray[]);

}
// ---------------

//C++ source code
// ---------------

void DLL_EXPORT __cdecl CalcAirProperties(int InputCombination, double Input1, double Input2, double Pressure,double PropertyArray[])
{
double *AirProperties = new double[7];

//Do Calculations

for(int i =0;i<7;i++)
{
PropertyArray(i) = AirProperties(i);
}

}

// ---------------

Here is my FORTRAN code:
!********************

PROGRAM ProgramMain

USE Statements
USE iso_c_binding, ONLY : c_ptr,c_double,c_f_pointer

IMPLICIT NONE

TYPE(c_ptr) :: c_p
REAL(c_double), POINTER :: f_p(:)

INTERFACE

SUBROUTINE CalcAirProperties(InputComb, InpValue1,InpValue2,BarometricPressure,PropertyArray) BIND(C,NAME='CalcAirProperties')

USE ISO_C_BINDING

INTEGER(kind=C_INT), INTENT(IN) :: InputComb
REAL(kind=C_DOUBLE), INTENT(IN) :: InpValue1
REAL(kind=C_DOUBLE), INTENT(IN) :: InpValue2
REAL(kind=C_DOUBLE), INTENT(IN) :: BarometricPressure

REAL(kind=C_DOUBLE), DIMENSION(7), INTENT(OUT) :: PropertyArray

END SUBROUTINE

END INTERFACE

REAL :: TempDB_Test
REAL :: TempRH_Test
REAL :: BaroPressure
REAL(kind=C_DOUBLE), DIMENSION(7) :: PropertyArray

TempDB_Test = 308.15
TempRH_Test = 0.69
BaroPressure = 101.325

CALL CalcAirProperties(2, TempDB_Test,TempRH_Test,BaroPressure,PropertyArray)

RHiC = PropertyArray(3)
RhoAiC = PropertyArray(7)

END ProgramMain

!********************

The above method also did not work. So I am kind of lost. I am still a newbie when it comes to mixed language programming.

I understand this could not be a problem with Simply Fortran IDE, but I would appreciate any help in this matter from the FORTRAN experts in this forum.

p.s: Do not ind the array element noted by normal parenthesis instead of square parenthesis. The forum would not accept square parenthesis.

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Calling a function in C++ dll from FORTRAN