How to pass float from C # to C ++ (dll) correctly

Question

I get huge differences when passing float from C # to C ++. I go through a dynamic float that changes over time. With the debugger, I get the following:

c++ lonVel    -0.036019072    float
c#  lonVel    -0.029392920    float

I installed my MSVC ++ 2010 floating point model in / fp: fast, which should be the standard in .NET, if I'm not mistaken, but that didn't help.

Now I can’t give out the code, but I can show part of it.

From the C # side, it looks like this:

namespace Example
{
    public class Wheel
    {       
        public bool loging = true;
        #region Members     
        public IntPtr nativeWheelObject; 
        #endregion Members

        public Wheel()
        {           
            this.nativeWheelObject = Sim.Dll_Wheel_Add();
            return;
        }

        #region Wrapper methods 
        public void SetVelocity(float lonRoadVelocity,float latRoadVelocity {
              Sim.Dll_Wheel_SetVelocity(this.nativeWheelObject, lonRoadVelocity, latRoadVelocity);
        }
        #endregion Wrapper methods
    }

    internal class Sim
    {
        #region PInvokes
        [DllImport(pluginName, CallingConvention=CallingConvention.Cdecl)]
                public static extern void Dll_Wheel_SetVelocity(IntPtr wheel,
                     float lonRoadVelocity, float latRoadVelocity);
        #endregion PInvokes 
    }       
}

And on the C ++ side @ exportFunctions.cpp:

EXPORT_API void Dll_Wheel_SetVelocity(CarWheel* wheel, float lonRoadVelocity,
     float latRoadVelocity) {
        wheel->SetVelocity(lonRoadVelocity,latRoadVelocity);
}

So, any suggestions on what I should do to get 1: 1 results, or at least 99% of the correct results.

Answer 1

, , http://msdn.microsoft.com/en-us/library/c151dt3s.aspx

, .

. : http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm

, "AlmostEqual", .

Answer 2

, havent , , , /fp: fast /arch: SSE2 !

, :

latRoadVelocity -0.15862428 float
lonRoadVelocity -0.036250707    float
wheel->latRoadVelocity  -0.15102120 float
wheel->lonRoadVelocity  -0.036250707    float

, lonRoadVelocity 1:1, latRoadVelocity. , 1:1 -.