Calling a C Struct from a LV CallLibrary Function.

[MogaRaghu]

I have a DLL called Canopen.dll.

I have an example C-Code on how to use the functions in the DLL.

Have been able to call a few of the functions in LV using the Call Library Function.

But one function is a problem as its arguments are from a Struct. It goes like this:

Function Call
short CMA_ConfigCANChannel(
unsigned char usChannelHandle,
CMA_CAN_CONFIG stCANConfig);

Parameter List

typedef struct
{
unsigned char ucBaudrate;
unsigned char ucPresc;
unsigned char ucSjw;
unsigned char ucTSeg1;
unsigned char ucTSeg2;
unsigned char ucAccCode;
unsigned char ucAccMask;
} CMA_CAN_CONFIG;

Now how to convert this to be suitable fro CallLibrary Function ?? (  Actually there is one example in the NI site but that is in LV5.0 and my LV2009 cannot open it !!)

Thanks

[smercurio_fc]

Create a cluster consisting of U8 integers. You will need to use 8 of them since the struct has 7 and you will need to make sure you account for alignment to memory locations. You can then just use "Adapt to Type" for the parameter type. LabVIEW comes with a very detailed example on calling DLLs. Open the Example Finder and search for "DLL".

[Julien_31]

Hi,

I'm not sure but I suggest you use a cluster (a LabVIEW Cluster is equivalent to a C Struct).

So in your case, you may pass a 7 item cluster to your "call library function node" (cluster containing ucBaudrate, ucPresc, etc...).

Hope this helps.

Best,

J.

[Julien_31]

Oups, smercurio answered before I post my answer. I think it's explanation is most complete than mine. 🙂

[nathand]

Unfortunately I think smercurio's answer is incorrect in this case.  Rolfk answered this question here.  To pass a struct by value, create one parameter for each element of the struct.

[smercurio_fc]

You know, I didn't even see it was being passed by value. Guess it's habit for me to always see it passed by reference.

[Kousy]

How to handle int array  and string array inside a C structure to call it from LV call library function?

Function:

short CMA_GetVersion( unsigned char ucChannelHandle, CMA_VersionStruct *stpVersion);

C Structure:
typedef struct
{
unsigned long ulHWSerialNumber;
unsigned char ucHWMainRevision;
unsigned char ucHWSubRevision;
unsigned char ucHWIdentString[18];
unsigned char ucSWMajorVersion;
unsigned char ucSWMinorVersion;
unsigned char ucSWBuild;
} CMA_VersionStruct;

Function:

short CMA_InstallPDO_E( unsigned char ucChannelHandle, CMA_PDOConfig, unsigned short *uspPDOHandle);

C Structure:
typedef struct
{
unsigned char ucPDOType;
unsigned long ulCOBID;
unsigned char ucTransType;
unsigned char ucAccType;
unsigned char ucEventNotif;
unsigned char ucaDefVal[8];
unsigned short usEventTimer;

unsigned char ucNrOfByte;

unsigned char ucNoInitTrans;
} CMA_PDOConfig;

Hope someone helps.

Thanks

Kousy

[nathand]

This has been asked over and over again on this forum.  You need to replace the array in the C struct with a LabVIEW cluster containing the same number of elements.  For example, you would replace ucHWIdentString[18] with a cluster of 18 U8 values.  The easiest way to generate such a cluster is by wiring an empty array of U8 to "Array to Cluster" and setting the number of cluster elements appropriately.  Create a control or constant as necessary from the output of Array to Cluster.  To get a string into that structure, you can use String to Array of U8, followed by Array to Cluster.  The reverse operation will get the you the string out of that structure.

[Kousy]

nathand,

I have tried Adapt to Type and Handle by value for the above mentioned functions. Still Im getting LV Error 1097 when trying out GetVersion function call and Functional Error of -110 when trying out InstallPDO_E. Im attaching the VI. Can you please look into it?

Thanks

Kousy

[nathand]

Based on the random clusters floating around your block diagram, it looks like you tried everything except the one thing I suggested.  Create a cluster that matches your C structure, and replace the fixed-size arrays with equivalent clusters.  For the CMA_VersionStruct, that means that ucHWIdentString should be replaced with a cluster containing 18 U8 values (U8 is the same size as char).  Then pass the entire CMA_VersionStruct cluster as a single parameter set to Adapt to Type (the Data Format doesn't matter), because you want to pass it by reference, not by value.