Passing a cluster between C++ DLL and LV

[jdubb9]

Hi there,

I am writing an application that is passing a simple cluster of doubles and an int from a C++ DLL to LV.  I have used the Call_DLL.vi as reference.  The values getting returned in the cluster are not the same as those returned to LV using a bunch of get() routines.

Here is the C code that uses the structure:

typedef struct {

double Distance; /* Distance measured in millimeters */

 int BitSet; /* Measurement error flag, as follows:

0 = no error

2 = too close to target or bad signal

4 = too far from target or signal is too noisy

FF = unknown */

 double XPos;

double YPos;

double ZPos;

double RotMat11;

double RotMat12;

double RotMat13;

double RotMat21;

double RotMat22;

double RotMat23;

double RotMat31;

double RotMat32; double RotMat33;

} Data;

_declspec(dllexport) int System_Single_Measurement(Data *Input, Data *Return_Struct){

 

Return_Struct->Distance = Measure.Distance;

Return_Struct->BitSet = (int)Measure.BitSet; 

//does stuff to fill the Postion[] and RotMatrix[] arrays.

 

Return_Struct->XPos = Position[0];

Return_Struct->YPos = Position[1];

Return_Struct->ZPos = Position[2];

Return_Struct->RotMat11 = RotMatrix[0][0];

Return_Struct->RotMat12 =RotMatrix[0][1];

Return_Struct->RotMat13 = RotMatrix[0][2];

Return_Struct->RotMat21 = RotMatrix[1][0];

Return_Struct->RotMat22 = RotMatrix[1][1];

Return_Struct->RotMat23 = RotMatrix[1][2];

Return_Struct->RotMat31 = RotMatrix[2][0];

Return_Struct->RotMat32 = RotMatrix[2][1];

Return_Struct->RotMat33 = RotMatrix[2][2];

 return 1;

}

An example of a get() routine:

_declspec(dllexport) double Camera_GetXPosition(){

return Position[0];

}

I have attached the VI we are using as well.

It is possible that there is some weird glitch in the rest of the C code, but since the values returned by the get() methods are correct, it seems likely that I have messed up returning the cluster.

Thanks!

[Andrey_Dmitriev]

At the first try to add #pragma pack(1) before struct typedef. I'm not sure which defaults are used by your compiler, but you may have 4 bytes gap between int BitSet and double XPos members.

If you can't change your C code, then try to insert "int Dummy " between int BitSet and double XPos.

Andrey.

Message Edited by Andrey Dmitriev on 03-26-2010 10:35 AM