I am calling a Fortran DLL from Excel VBA, and have ben doing so successfully for years.

Now one of our engineering suppliers is using a 64-bit version of Office (we haven't migrated from Office 2007 yet).

Can someone help me with my interfaces?

I am using calls like

Private Declare Sub ApproxBayerDensity_F Lib "AHEAProps.dll" (TempC As Double, Value As Double, ByVal Units As String)

Call ApproxBayerDensity_F(T, Value, Units)

the Fortran side is like

Subroutine ApproxBayerDensity_F(TempC, Value, Units)

!DEC$ ATTRIBUTES DLLEXPORT, STDCALL, ALIAS:'ApproxBayerDensity_F' :: ApproxBayerDensity_F

!DEC$ ATTRIBUTES REFERENCE :: Units

...

IMPLICIT NONE

Real (KIND=8),INTENT(IN) :: TempC(1)

Real (KIND=8),INTENT(OUT) :: Value(1)

Character (LEN=20),INTENT(INOUT) :: Units

...

For the 64-bit interface, I now need to use

Private Declare PtrSafe Sub ApproxBayerDensity_F Lib "AHEAProps.dll" (TempC As Double, Value As Double, ByVal Units As String)

Where the variables have to be compatible with the 64-bit Excel. 

Do I need to change anything on the Fortran side?

Thanks,

David