topic problem with function returns from c++ in Intel® Fortran Compiler

problem with function returns from c++

jim_cox — Wed, 15 Mar 2017 11:01:33 GMT

Hopefully this should be easy...

I'm using fortran to call a c++ function.

This function returns the value 2 as a long - debugging shows this being set

But when it comes back into my integer4 fortran variable I see the return value as -2147483648

Any thoughts about what might be going wrong?

Very grateful for any assistance.

Can you show the code? It is

Arjen_Markus — Wed, 15 Mar 2017 11:07:15 GMT

Can you show the code? It is very likely a mismatch in the interface as seen from both sides.

fortran looks like:

jim_cox — Wed, 15 Mar 2017 11:13:48 GMT

fortran looks like:

INTEGER*4 LNS

LNS = SIDGETLANECT(%val(J2))

c++

long __stdcall SIDGETLANECT(long origin)
{
   CComPtr<ISIAPILegs> legs = NULL;
   CComPtr<ISIAPILeg> leg = NULL;
   CComPtr<ISIAPILaneApproachs> laneApprs = NULL;
   CComPtr<ISIAPILaneApproach> laneAppr = NULL;
   long b;

site->get_Legs(&legs);
legs->get_Count(&b);

leg = NULL;

legs->get_Item(long (origin - 1) , &leg);

   if (leg == NULL) return 0;
   else
   {
       long laneApprCount, laneno;
       VARIANT_BOOL laneDisciplineExisting = false;

leg->get_LaneApproachs(&laneApprs);
laneApprs->get_Count(&laneApprCount);

       return laneApprCount ;

   }
}

But does the Fortran compiler

Arjen_Markus — Wed, 15 Mar 2017 11:42:32 GMT

But does the Fortran compiler "know" that SIDGETLANECT is an integer function?

If you do not declare it as such, via an interface block for instance, the default typing rules kick in an the function will be considered to return a floating-point number.

Try:

interface

integer function SIDGETLANECT(origin)

integer, value :: origin

end function

end interface

or the like

You should also declare the C

jimdempseyatthecove — Wed, 15 Mar 2017 11:55:19 GMT

You should also declare the C++ function as

extern "C" { long SIDGETLANECT(long origin); } // function prototype

See the IVF documentation: C/C++ Naming Conventions.
See also section under BIND

Jim Dempsey

jim_cox — Wed, 15 Mar 2017 16:44:14 GMT

Sorry, its after midnight here and I probably should have also mentioned that

the c++ function is in a separate library

and

that it has a .h function declaration

extern "C" long __stdcall SIDGETLANECT(long origin);

I will take a look at the interface definition in the morning

Thanks for your input

Jim