How to call a C pointer from call library function node

I have a client/server application which the client I am trying to develop using Labview. When I use to communicate the server and the client using the program provided by the manufacter, the system works perfectly.
Now, I am trying to develop a system using labview, because I need to get another things.
I have the DLL provided by the manufacter and the .h too, so I can check the functions parameters. One of these functions needs to be called using a struct element. Probably, the function's DLL instantiates the elements of this struct. I use the call library function node to do it.
When I receive the data, the function returns to me the struct that I passed as a parameter before, and then I can read all the elements of the struct, except the string element that returns nothing. The struct elements that are numerical, I can read them perfectly.
Another thing that is important to say, is that the string data was not returned in fact by the DLL function that the system calls. I have to pass a pointer (I use it as unsigned 16 in Labview, but I tried before as string and unsigned 8) as a parameter, and this pointer will point to the memory location that the string is. When I try to read what is returned by the function, I can read nothing. The same function returns that the size of data that is returning is 17 bytes.
How can I solve it?
Thank you in advance

Did you take a look at the example that ships with LabVIEW that shows how to do all sorts of data passing to DLLs. I believe your situation is one of the examples listed. You can find the example VI in the "<LabVIEW install directory>\examples\dll\data passing" directory.

Similar Messages

How to implement a callback function using LabView's Call Library Function Node?

I am trying to call a fuction from a SDK.dll library using the Call Library Function Node. The SDK was provided to
me and I do not have the source code, just the .dll and .h files.
The SdkSetPropertyEventHandler function has a callback fuction as one of its parameters. How do I implement the
callback using the CLF node? I am a good LabView programmer but this is my first time using the Call Library
Function Node. I have read all the info I can find on NI's web site and the discussion board but cannot figure
this one out. I am using LabView 8.6.
The SDK.h deacribes the function as:
// Function:   SdkSetPropertyEventHandler
SdkError SDKAPI SdkSetPropertyEventHandler(
            SdkCameraRef                    inCameraRef,
            SdkPropertyEvent                inEvnet,
            SdkPropertyEventHandler         inPropertyEventHandler,
            SdkVoid*                        inContext );
// Description:
//       Registers a callback function for receiving status
//          change notification events for property states on a camera.
// Parameters:
//       In:    inCameraRef - Designate the camera object.
//              inEvent - Designate one or all events to be supplemented.
//              inPropertyEventHandler - Designate the pointer to the callback
//                      function for receiving property-related camera events.
//              inContext - Designate application information to be passed by
//                      means of the callback function. Any data needed for
//                      your application can be passed.
//      Out:    None
// Returns:    Any of the sdk errors.
A separate header file called SDKTypes.h contains the following data:
typedef SdkUInt32 SdkPropertyEvent;
typedef SdkUInt32 SdkPropertyID;
typedef void       SdkVoid;
typedef struct __SdkObject*    SdkBaseRef;
typedef SdkBaseRef    SdkCameraRef;
SdkPropertyEventHandler
typedef SdkError ( SDKCALLBACK *SdkPropertyEventHandler )(
                    SdkPropertyEvent        inEvent,
                    SdkPropertyID           inPropertyID,
                    SdkUInt32               inParam,
                    SdkVoid *               inContext );
Thanks for your help.
Alejandro
Solved!
Go to Solution.

alejandroandreatta wrote:
I am trying to call a fuction from a SDK.dll library using the Call Library Function Node. The SDK was provided to
me and I do not have the source code, just the .dll and .h files.
The SdkSetPropertyEventHandler function has a callback fuction as one of its parameters. How do I implement the
callback using the CLF node? I am a good LabView programmer but this is my first time using the Call Library
Function Node. I have read all the info I can find on NI's web site and the discussion board but cannot figure
this one out. I am using LabView 8.6.
Basically you do not do that. LabVIEW does not know pointers and certainly not function pointers. What you should do instead is writing a C DLL that implements the callback and also exports a function to be called by LabVIEW that translates between the callback and a LabVIEW user event. Look for PostLVUserEvent() here on the NI site to find examples how to do that.
Rolf Kalbermatter
Message Edited by rolfk on 02-11-2009 08:00 PM
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

Call library function node with array of clusters using array data pointer

Hello all.
I am writing a LabVIEW wrapper for an existing DLL function.
The function has, as one of its parameters, an array of structs. The struct is very simple, containing two integers. I am using the call library function node to access it.
In Labview I created an array of clusters, where the cluster has two 32-bit integers as its members. So far, so good.
Now I have to pass this in to the Call Library Function Node. Here I am running into trouble.
I have used The topic in LAVA and The topic in the knowledge base as my primary sources of information, though I have read a bunch of forum topics on the subject too.
I do understand that I could write a new function which takes as a parameter a struct with the size as the first member and an array as the second, and I might just do this and have it call the regular function, but I was hoping to do it more simply.
According to the C file which LabVIEW generates for me from the CLFN when I choose "Adapt to Type" and "Array Data Pointer", the prototype it is expecting is:
int32_t myFunc(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, void data[], int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex);
And the prototype of the function in my DLL is
int borland_dll myFunc(DWORD handle, usint channel,
int FIFOnumber, struct mStruct *data, int numWords, int *actualLoaded, int *actualStartIndex);
This looks like a match to me, but it doesn't work (I get garbage in data). From the topic in LAVA referenced above, I understood that it would work. It does not.
If I cast data to the pointer-to-pointer I get when I generate c code by wiring my struct to a CIN and generating, then I seem to get what I expect. But this seems to work when I choose "pointers to handles" too, and I would expect array data pointer to give a different result.
Is there any way to get this to work directly, or will I have to create a wrapper? (I am currently using LabVIEW 2011, but we have customers using 2009 and 2012, if not other versions as well).
Thank you.
Batya
Solved!
Go to Solution.

OK, here is more detailed information.
I have attached the VI.
This is the code from the "C" file created by right-clicking the CLN and creating a "C" file.
When the parameter in the CLN is set to "array data pointer":
/* Call Library source file */
#include "extcode.h"
int32_t Load_Transmit_FIFO_RTx(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, void data[], int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex);
int32_t Load_Transmit_FIFO_RTx(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, void data[], int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex)
/* Insert code here */
When the parameter is "pointers to handles":
/* Call Library source file */
#include "extcode.h"
/* lv_prolog.h and lv_epilog.h set up the correct alignment for LabVIEW data. */
#include "lv_prolog.h"
/* Typedefs */
typedef struct {
int32_t control;
int32_t data;
} TD2;
typedef struct {
int32_t dimSize;
TD2 data[1];
} TD1;
typedef TD1 **TD1Hdl;
#include "lv_epilog.h"
int32_t Load_Transmit_FIFO_RTx(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, TD1Hdl *data, int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex);
int32_t Load_Transmit_FIFO_RTx(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, TD1Hdl *data, int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex)
/* Insert code here */
When the parameter is set to "handles by value":
/* Call Library source file */
#include "extcode.h"
/* lv_prolog.h and lv_epilog.h set up the correct alignment for LabVIEW data. */
#include "lv_prolog.h"
/* Typedefs */
typedef struct {
int32_t control;
int32_t data;
} TD2;
typedef struct {
int32_t dimSize;
TD2 data[1];
} TD1;
typedef TD1 **TD1Hdl;
#include "lv_epilog.h"
int32_t Load_Transmit_FIFO_RTx(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, TD1Hdl *data, int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex);
int32_t Load_Transmit_FIFO_RTx(uint32_t handle, uint16_t channel,
int32_t FIFOnumber, TD1Hdl *data, int32_t numWords, int32_t *actualLoaded,
int32_t *actualStartIndex)
/* Insert code here */
As to the DLL function, it is a bit more complicated than I explained above, in the current case. My VI calls the function by this name in one DLL, and that DLL loads a DLL and calls a function (with the same name) in the second DLL, which does the work. (Thanks Rolfk, for helping me with that one some time back!)
Here is the code in the first ("dispatcher") DLL:
int borland_dll Load_Transmit_FIFO_RTx(DWORD handle, usint channel, int FIFOnumber, struct FIFO_DATA_CONTROL *data, int numWords, int *actualLoaded, int *actualStartIndex)
t_DispatchTable *pDispatchTable = (t_DispatchTable *) handle;
int retStat = 0;
retStat = mCheckDispatchTable(pDispatchTable);
if (retStat < 0)
return retStat;
if (pDispatchTable->pLoad_Transmit_FIFO_RTx == NULL)
return edispatchercantfindfunction;
return pDispatchTable->pLoad_Transmit_FIFO_RTx(pDispatchTable->handlertx, channel, FIFOnumber, data, numWords, actualLoaded, actualStartIndex);
borland_dll is just "__declspec(dllexport)"
The current code in the DLL that does the work is:
// TEMP
typedef struct {
int control;
int data;
} TD2;
typedef struct {
int dimSize;
TD2 data[1];
} TD1;
typedef TD1 **TD1Hdl;
// END TEMP
int borland_dll Load_Transmit_FIFO_RTx(int handlertx, usint channel, int FIFOnumber, struct FIFO_DATA_CONTROL *data, int numWords, int *actualLoaded, int *actualStartIndex){
struct TRANSMIT_FIFO *ptxFIFO; //pointer to transmit FIFO structure
usint *pFIFOlist; //pointer to array of FIFO pointers to FIFO structures
int FIFOentry, numLoaded;
usint *lclData;
usint nextEntryToTransmit;
// TEMP
FILE *pFile;
int i;
TD1** ppTD = (TD1**) data;
TD1 *pTD = *ppTD;
pFile = fopen("LoadFIFOLog.txt", "w");
fprintf(pFile, "Starting Load FIFO with %d data words, data pointer 0x%x, with the following data&colon; \n", numWords, data);
for (i = 0; i < numWords; i++) {
fprintf(pFile, "%d: control--0x%x, data--0x%x \n", i, data[i].control, data[i].data);
fflush(pFile);
fprintf(pFile, "OK, using CIN generated structures: dimSize %d, with the following data&colon; \n", pTD->dimSize);
for (i = 0; i < numWords; i++) {
fprintf(pFile, "%d: control--0x%x, data--0x%x \n", i, pTD->data[i].control, pTD->data[i].data);
fflush(pFile);
// END TEMP
if ((handlertx) <0 || (handlertx >= NUMCARDS)) return ebadhandle;
if (cardrtx[handlertx].allocated != 1) return ebadhandle;
pFIFOlist = (usint *) (cardrtx[handlertx].segaddr + cardrtx[handlertx].glob->dpchn[channel].tr_stk_ptr);
pFIFOlist += FIFOnumber;
ptxFIFO = (struct TRANSMIT_FIFO *)(cardrtx[handlertx].segaddr + *pFIFOlist);
//use local copy of ptxFIFO->nextEntryToTransmit to simplify algorithm
nextEntryToTransmit = ptxFIFO->nextEntryToTransmit;
//on entering this routine nextEntryToLoad is set to the entry following the last entry loaded
//this is what we need to load now unless it's at the end of the FIFO in which case we need to wrap around
if ( ptxFIFO->nextEntryToLoad >= ptxFIFO->numEntries)
*actualStartIndex = 0;
else
*actualStartIndex = ptxFIFO->nextEntryToLoad;
//if nextEntryToLoad points to the last entry in the FIFO and nextEntryToTransmit points to the first, the FIFO is full
//also if nextEntryToLoad == nextEntryToTransmit the FIFO is full and we exit without loading anything
if (( (( ptxFIFO->nextEntryToLoad >= ptxFIFO->numEntries) && (nextEntryToTransmit == 0)) ||
( ptxFIFO->nextEntryToLoad == nextEntryToTransmit)) && (ptxFIFO->nextEntryToLoad != INITIAL_ENTRY)){
*actualLoaded = 0; //FIFO is full already, we can't add anything
return 0; //this is not a failure, we just have nothing to do, this is indicated in actualLoaded
numLoaded = 0;
lclData = (usint *)data; //must use 16 bit writes to the module
//conditions are dealt with inside the for loop rather than in the for statement itself
for (FIFOentry = *actualStartIndex; ; FIFOentry++) {
//if we reached the end of the FIFO
//if the module is about to transmit the first element of the FIFO, the FIFO is full and we're done
//OR if the module is about to transmit the element we're about to fill in, we're done - the
//exception is if this is the first element we're filling in which means the FIFO is empty
if ((( FIFOentry >= ptxFIFO->numEntries) && (nextEntryToTransmit == 0)) ||
((FIFOentry == nextEntryToTransmit) && (FIFOentry != *actualStartIndex) )){
*actualLoaded = numLoaded;
//set nextEntryToLoad to the end of the FIFO, we'll set it to the beginning next time
//this allows us to distinguish between full and empty: nextEntryToLoad == nextEntryToTransmit means empty
ptxFIFO->nextEntryToLoad = FIFOentry;
return 0;
//we reached the end but can continue loading from the top of the FIFO
if ( FIFOentry >= ptxFIFO->numEntries)
FIFOentry = 0;
//load the control word
ptxFIFO->FifoData[FIFOentry * 3] = *lclData++;
//skip the high of the control word, the module only has a 16 bit field for control
lclData++;
//now put in the data
ptxFIFO->FifoData[(FIFOentry * 3) + 2] = *lclData++;
ptxFIFO->FifoData[(FIFOentry * 3) + 1] = *lclData++;
numLoaded++;
//we're done because we loaded everything the user asked for
if (numLoaded >= numWords) {
*actualLoaded = numLoaded;
ptxFIFO->nextEntryToLoad = FIFOentry+1;
return 0;
//if we reached here, we're done because the FIFO is full
*actualLoaded = numLoaded;
ptxFIFO->nextEntryToLoad = FIFOentry;
fclose (pFile);
return 0;
As you can see, I added a temporary diagnostic with the structures that were created in the "Handles by value" case, and print out the data. I see what is expected, whichever of the options I pick in the CLN!
I understood (from the information in the two links I mentioned in my original post, and from the name of the option itself) that "array data pointer" should pass the array of data itself, without the dimSize field. But that does not seem to be what is happening.
Batya
Attachments:
ExcM4k Load Transmit FIFO.vi ‏15 KB

How can I stop power point from opening each time my Macbook Pro starts?

How can I stop power point from opening each time my Macbook Pro starts?

Remove it from the list in Startup Items (System Preferences).

Calling a library function node much faster than labview code?

Hi, I wrote a labview routine to perform a multiple tau autocorrelation on a large array of integers. A multi tau autocorrelation is a way to reduce the computation time of the correlation but at the expense of resolution. You can taylor the multitau correlation to give you good resolution where you need it. For instance, I require good resolution near the middle (the peak) of the correlation, so I do a linear autocorrelation for the first 64 channels from the peak, then I skip every second channel for the next 32, then skip every 4th channel for 32 more, then skip every 8th for 32 channels... etc.
Originally, I wrote my own multitau calculation, but it took several hours to perform for just 1024 channels of the correlation of around 2million points of data. I need to actually do the the correlation on probably 2 billion or more points of data, which would take days. So then I tried using labview's AutoCorrelation.vi which calls a library function. It could do a linear autocorrelation with 4 million points in less than a minute. I figured that writing my code in C and calling it using a call library function node would be faster, but that much faster?
Finally, I wrote some code that extracts the correlation data points that I would've got from my multitau code from the linear correlation function that I get from the AutoCorrelation.vi. Clearly this is not optimal, since I spend time calculating all those channels of the correlation function just to throw them away in the end, but I need to do this because the final step of my procedure is to fit the correlation function to a theoretical one. With say 2million points, the fit would take too long. The interesting thing here is that simply extracting the 1024 point from the linear autocorrelation function takes a significant amount of time. Is labview really that slow?
So, my questions are... if I rewrite my multitau autocorrelation function in C and call it using a call library function node, will it run that much faster? Can I achieve the same efficiency if I use a formula node structure? Why does it take so long just to extract 1024 points from an array?
I've tried hiding indicators and this speeds things up a little bit, but not very much.
I'll attach my code if you're interested in taking a look. There is a switch on the front panel called 'MultiTau'... if in the off position, the code performs the linear autocorrelation with the AutoCorrelation.vi, if in the on position, it performs a multitau autocorrelation using the code I wrote. Thanks for any help.
Attachments:
MultiTauAutocorrelate.vi ‏627 KB

Hi,
The C routine that AutoCorrelation.vi is using is probably a higly optimised routine. If you write a routine in LabVIEW, it should be less then 15% slower. But you'd have to know all ins and outs of LabVIEW. How data is handled, when memory is allocated, etc. Also note that the AutoCorrelation.vi has years of engineering behind it, and probably multiple programmers.
It might even be possible that the c code uses an algorithmic improvement, like the Fast Fourier Transform improves speed on the Fourier Transform. I think the autocorrelation can be done using FFT, but that isn't my thing, so I'm not sure.
For a fair comparation, posting the code in this forum was a good idea. I'm sure together we can get it to 115% or less of the C variant. (15/115 is just a guess, btw)
I'm still using LV7.1 for client compatibility, so I'll look at the code later.
Regards,
Wiebe.
"dakeddie" <[email protected]> wrote in message news:[email protected]...
Hi,  I wrote a labview routine to perform a multiple tau autocorrelation on a large array of integers.  A multi tau autocorrelation is a way to reduce the computation time of the correlation but at the expense of resolution.  You can taylor the multitau correlation to give you good resolution where you need it.  For instance, I require good resolution near the middle (the peak) of the correlation, so I do a linear autocorrelation for the first 64 channels from the peak, then I skip every second channel for the next 32, then skip every 4th channel for 32 more, then skip every 8th for 32 channels... etc. Originally, I wrote my own multitau calculation, but it took several hours to perform for just 1024 channels of the correlation of around 2million points of data.  I need to actually do the the correlation on probably 2 billion or more points of data, which would take days.  So then I tried using labview's AutoCorrelation.vi which calls a library function.  It could do a linear autocorrelation with 4 million points in less than a minute.  I figured that writing my code in C and calling it using a call library function node would be faster, but that much faster?Finally, I wrote some code that extracts the correlation data points that I would've got from my multitau code from the linear correlation function that I get from the AutoCorrelation.vi.  Clearly this is not optimal, since I spend time calculating all those channels of the correlation function just to throw them away in the end, but I need to do this because the final step of my procedure is to fit the correlation function to a theoretical one.  With say 2million points, the fit would take too long.  The interesting thing here is that simply extracting the 1024 point from the linear autocorrelation function takes a significant amount of time.  Is labview really that slow?So, my questions are...  if I rewrite my multitau autocorrelation function in C and call it using a call library function node, will it run that much faster?  Can I achieve the same efficiency if I use a formula node structure?  Why does it take so long just to extract 1024 points from an array?I've tried hiding indicators and this speeds things up a little bit, but not very much.I'll attach my code if you're interested in taking a look.  There is a switch on the front panel called 'MultiTau'... if in the off position, the code performs the linear autocorrelation with the AutoCorrelation.vi, if in the on position, it performs a multitau autocorrelation using the code I wrote.  Thanks for any help.
MultiTauAutocorrelate.vi:
http://forums.ni.com/attachments/ni/170/185730/1/MultiTauAutocorrelate.vi

[HELP] Call Library Function Node...

I have a DLL which has a function as follows:
int GetMessageNameNumber (char* messageName [], const int MessageNumber);
The function is used thus:
char *MessageName = NULL;
int MessageNumber = 0;
error = HL1553API_GetMessageNumberName (&MessageName, MessageNumber);
MessageName will then contain the message name as a string.
I having the devils own job trying to wrap this into a Labview module. I have a Call Library function node for the above function, but I am not sure what to set the "MessageName" parameter too! I have tried Array of signed 8-bit integers, Adapt to Type, Array Data Pointer and then passed in a String array. Whatever I do results in LabView crashing. I know HL1553API_GetMessageNumberName works, because if I call it directly in TestStand it works fine. I need it LabView though!
Any ideas?
Christopher Povey
Senior Test Systems Engineer for BAE Systems.
Solved!
Go to Solution.

In C a pointer to a string or an array of strings are completely ambigues.
char ** something ===== char * something [].
You can not tell the two apart from the syntax but only from the documentation or from an example showing how the function is called. A C compiler treats the two equal in terms of access (but a C++ compiler will make a syntactic distinguishment when syntax checking code, resulting in possible compile warnings when prompted to use a sufficiently high warning level.)
The sample shows that this is not an array of strings that gets allocated by the caller and passed to the function, but a string pointer that gets passed by reference. As such the function will allocate a pointer and return it (a highly non-standard C practice at least for strings). This automatically begs the question when and how will this pointer be deallocated? The documentation for that function should document the memory manager call used to allocate that pointer and also point out the function to call to deallocate it. Ideally the library (DLL) provides a specific exported function for that purpose.
Assuming everything I have talked about so far is clear and available you have to trick LabVIEW a bit. You have to configer a pointer sized integer that gets passed by reference. Now this integer in the diagram IS in fact your string. If you only need to pass this pointer to other Call Library functions you are already done. Otherwise if you need to access the contents of that string from the LabVIEW diagram, you have to copy the information of that string pointer into a real LabVIEW string.
One way to do that is to use the MoveBlock() C function export that LabVIEW exports itself. I have explained this several times here on this forum and a search for MoveBlock will without doubt uncover those posts.
Another slightly better way is to use the LStrPrintf() function that LabVIEW also exports. For that you configure a Call Library function as follows:
Library name: LabVIEW
Function name: LStrPrintf
Calling convention: C
Threading: both are possible but the function is thread safe so just use reentrant
return parameter: int32 (this is a possible LabVIEW manager error code)
1st parameter: LabVIEW string handle, passed by value
2nd parameter: C string pointer
3rd parameter: pointer sized integer, passed by valu
Wire an empty string constant to the first parameter.
Wire a constant containing the text "%s" without quotes to the 2nd.
Wire your string pointer to the 3rd
On return the function will either return 0 as return value and the contents of the string on the output side of the 1st parameter or a non-zero return value indicating an error.
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

Using Call Library Function Node To Return C++ Structure Information

Hi everyone. This question is for all you LabVIEW gurus out there.
I am trying to call a function from a .dll to get information from a structure about a device (FT232H chip). I am using the "Call Library Function Node" to do this in LabVIEW. My issue is I do not know how to set up the "Call LIbrary Function Node" parameter for a C++ structure. How do I set up the pointer to FT_DEVICE_LIST_INFO_NODE structure using the "Call Library Function Node" so that I can read back the device information?
The details of the C++ function and the structure are below.
Thanks for everyone's help!
The C++ function is the following:
FT_STATUS I2C_GetChannelInfo (uint32 index, FT_DEVICE_LIST_INFO_NODE *chanInfo)
In = index (Index of the channel)
Out = *chanInfo (Pointer to FT_DEVICE_LIST_INFO_NODE structure)
The pointer to the FT_DEVICE_LIST_INFO_NODE is defined as:
typedef struct _FT_DEVICE_LIST_INFO_NODE {
ULONG Flags;
ULONG Type;
ULONG ID;
DWORD LocId;
char SerialNumber[16];
char Description[64];
FT_HANDLE ftHandle;
} FT_DEVICE_LIST_INFO_NODE;

Dennis/Nathan,
I tried to set up the "Call Library Function Node (CLFN)" correctly in order to read out Device Information from a FTDI Chip (FT232H) but when I run the VI LabVIEW crashes on me always.
I have attached the code. For the FT_DEVICE_LIST_INFO_NODE structure I passed into the "CLFN" a constant cluster of all the structure elements and then I set up the node to:
Type: Adapt to Type
Data format: Handles by Value
I think LabVIEW crash may have something to do with the fact that the output of the dll function is using a pointer to a structure. With the Handles by value Data format I am unable to set the Pointer to structure.
Can you please take a quick look at the code to see if I am setting the CLFN up correctly?
Thanks!
Once again, here are the C++ Code Details:
FT_STATUS I2C_GetChannelInfo (uint32 index, FT_DEVICE_LIST_INFO_NODE *chanInfo)
In = index (Index of the channel)
Out = *chanInfo (Pointer to FT_DEVICE_LIST_INFO_NODE structure)
The pointer to the FT_DEVICE_LIST_INFO_NODE is defined as:
typedef struct _FT_DEVICE_LIST_INFO_NODE {
ULONG Flags;
ULONG Type;
ULONG ID;
DWORD LocId;
char SerialNumber[16];
char Description[64];
FT_HANDLE ftHandle;
} FT_DEVICE_LIST_INFO_NODE;
Attachments:
FT_I2C_GetChannelInfo.vi ‏14 KB

Window doesn't close wheh Call Library Function Node set to Run in Any Thread

This is a problem regarding Call Library Function Nodes running in the UI thread or any thread.
I have a camera which has its own API supplied as a dll. I have created a set of VI wrappers which each call a function in the dll through a Call Library Function Node.
Initially each CLFN was set to 'Run in the UI thread' (the default).
To start the camera streaming images I call (through a CLFN)
ICubeSDK_Start(int CamIndex, Hwnd, ImgHandle, bool Preview, bool callback);
If Preview = True then the image is displayed in a preview window.
If ImgHandle = NULL a default preview window
is used.
In the CLFN definition I define:
ImgHandle as a U32
Preview as a I32
To stop the camera streaming images I call
ICubeSDK_Stop(int CamIndex)
In the actual implementation I set ImgHandle = 0 (NULL) and Preview = 1 (true).
This all works fine, and a preview window is opened and images displayed. When I call ICubeSDK_Stop the preview window is closed.
However, I would prefer to set the CLFN to 'Run in any thread' because
a) when run in the UI thread the preview window randomly gets sent to the back when I switch focus between open VI windows (presumably because it is in the same thread as the VIs)
b) I don't want to put unnecessary stuff in the UI thread
c) my (naive?) understanding is that it is safer to run in any thread
So I have set all CLFNs to 'Run in any thread'
When I do this the preview window opens OK, and behaves like any other non LabVIEW controlled window in terms of focus. But when I call ICubeSDK_Stop() the preview window does not get closed properly, it just shows a blank image. I can't close it manually, there is no X in the corner and no option to close it from the taskbar. To get rid of it I have to close the LabVIEW project it is spawned from, which often results in a crash. It does appear as a separate item in task manager but if I 'end process' it, LabVIEW closes (and often crashes) as well.
If I change only the CLFNs that call the Start and Stop functions back to 'Run in the UI thread' then it all works fine again, except that the preview window gets sent to the back randomly as before.
So, what do I have to do to get the preview window to close properly if I set the CLFN to 'Run in any thread'.
Alternatively, is there a way to close the window programmatically (ie force it to close) after I have called ICube_Stop.
Thanks
DAve

Hi Dave,
The "Run In UI Thread" switches from the thread the VIs currently executing in to the user interface thread. If you select "Run in Any Thread", the Call Library Function Node continues in the currently executing thread. By default, all Call Library Function Nodes run in the User Interface thread.
Before you configure the Call Library Function Node to run in any thread, you have to make sure that the code is thread safe. Code is thread safe when it does not store any global data (e.g. global variables, files on disks, etc.), does not access any hardware, does not make calls to any functions, libraries or drivers that are not thread safe.
Unfortunately, since you said that your DLL accesses hardware, it is not recommended to use "Run in Any Thread." This is probably why you are seeing the crash.
If your preview window gets sent to the back you can programmatically bring it forward. Here is an example of how this can be done: http://decibel.ni.com/content/docs/DOC-4551
If you want to completely close the window down you can do so as described in this link: http://digital.ni.com/public.nsf/allkb/81E9C1441900FFCE8625748F0055DBB0?OpenDocument
I also thought you might find this useful: http://zone.ni.com/devzone/cda/tut/p/id/3009
I hope this helps.
Regards,
Mahdieh G
Applications Engineer
National Instruments UK&Ireland

How do you use the windows User32.dll Library functions to read variables from other applications that are running

I am trying to read a text box from a programme running at the same time as my Labview application using calls to the Windows
User32.dll. I believe I need to find the window handle for the 'form' containing this text string and use this together with
various other defined input variables to access the sting.
I have no experience of using this 'Call Library Function Node', but have an understanding of the 'C' programming language. Does anyone have
example Labview code showing how this might be done.
Thanks

If you're trying to access information that's being displayed in the window of another application and that application has no ActiveX interface, then yes, Windows calls can be used. There's a very good example on calling DLLs that ship with LabVIEW. Open the Example Finder (Help->Find Examples) and switch to the Search tab. Enter "Call" in the search box and open the VI "Call DLL". Run the VI, select any of the examples, and click the "Open Example VI..." button. That shows you how to call a DLL.
Now, given that you have no experience in calling DLLs, have only an "understanding" of C (which to me means you have never written something like a DLL), and don't seem to know that much about what Windows functions you may need, you're going to find this route pretty difficult, especially since you have to deal with Windows API calls, which are not always that easy to do from LabVIEW.
Let me propose an alternate solution. Go over to http://www.autoitscript.com/autoit3/ and download AutoIt. This is an automation tool that allows you to automate just about anything you want. It has an ActiveX interface that you can call from LabVIEW. I've attached an example VI that shows you how to use it to get the value of a text box from one of the tabs in the computer "System Properties" control panel applet.
Attachments:
AutoIt Example (v7).vi ‏25 KB

Strange problem of calling library function node in labview 2010 and 2011

one year ago,I develop a program to usb device data and it works well,in labview 8.6 or 2009(win xp).Recently, When I test
the program in labview 2010 and labview 2011(win xp).,the program always crash immediately.I check the program and find main
problem is in call library function node. In my program,I use labview 2009 library for the USBExpress driver for
Silicon Labs USB MCU's from:https://decibel.ni.com/content/docs/DOC-9522,for example, 2 functions SI_OPEN and SI_READ
can not work well.
the header definition of SI_OPEN and SI_READ is:
SI_STATUS WINAPI SI_Open(
DWORD dwDevice,
HANDLE* cyHandle
SI_STATUS WINAPI SI_Read(
HANDLE cyHandle,
LPVOID lpBuffer,
DWORD dwBytesToRead,
LPDWORD lpdwBytesReturned,
OVERLAPPED* o = NULL
the SI_STATUS is equivalent to int type.
orignally, for HANDLE * in SI_Open, the parameter type in call library function node is numeric, data format is unsigned 32 bit integer ,and pass pointer to value.
for HANDLE in SI_Read, the parameter type in call library function node is numeric, data format is unsigned 32 bit integer ,and pass value.The program works well in labview 8.6&2009,however,crash in labview 2010 &2011.
later,I debug the program, for HANDLE *, I choose parameter type in call library function node as adapt to type, data format is point to Handles.for HANDLE, I choose parameter type in call library function node as adapt to type, data format is Handles by Value.Crash not happend in labview 2010&2011,however,it cannot read any data from from USB device correctly as before.I can not find the reason.
Dear friends,I need your help to answer the problem. Thank you.

Based on the help page it looks like it should execute asynchronously.
The thing in the description that leads me to believe they execute asynchronously is that you can configure the library to run as a multi-threaded operation.
Please take a look here to see the difference between synchronous and asynchronous execution.
Since the code even has the ability to be multi-threaded, you can consider it as running in parallel to your other code.
Any data returned is passed to the thread that called that function.
Cory K

Call Library Function Node.vi using problem

Hi,
我用Labwindows 编了个读文件的程序然后生成动态库, 然后在LabVIEW里调用该动态库(Call Library Function Node), 即向该动态库传递文件名及路径和某一字符串,然后该动态库打开相应路径文件从中读出并返回三个参数值,可是每次的返回值总显示打开文件失败, 该函数在Labwindow里没有问题. 在LabVIEW里如何调试来确定传到动态库的参数格式是没有问题的呢?任何的指点迷津,不胜感激!
Frank,

xiejiezhou wrote:
Thank Georges and Rolf Kalbermatter,
I changed the runtime support with " Full Runtime Engine" instead of " LabVIEW Real-Time Only" before, it's work now, but the output parameters returned are irregular incorrect characters. My funciton prototype is:
DLLEXPORT long CollectParameter(char *NomFile, char *szNomParagraph, char *Command[], char *Type[], char *Value[])
so how to configure the type in LabVIEW respectively? I tried every types, just "c String Pointer" is ok, but returned value irregular & incorrect.
As Geogre's suggestion, i should add my code as below function generated by LabVIEW, is it?
ong CollectLabel(char szNomFile[], char szNomParagraph[], char Command[], char Type[], char Value[])
/* Insert code here */
Frank
The char *Command[], char *Type[], char *Value[] parameters are parameters that you can not create with LabVIEW. This are arrays of strings and and LabVIEW has a completely different idea about how to place strings and arrays in memory than what is used in C.
And while LabVIEW supports translation of the top level type to C compatible pointers it does not have any option to let you configure it to translate embedded elements in parameters (the strings in the array) to be translated too.
But to be honest what you seem want to do is read in a file, do some parsing and then return parameters taken out of that file. Doing that all in LabVIEW would be SOOOOOOOOOOOO much easier.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

LabVIEW PDA reports COREDLL.DLL error when using Call Library Function Node

I'm trying to build a LV PDA app that calls an external DLL file built using embedded visual C. When configuring the Call Library Function node I select the stub DLL, configure the I/O parameters and select OK. When the configuration dialog closes I get the following error:
LabVIEW: LabVIEW.exe - Unable to Locate Component
This application has failed to start because COREDLL.DLL was not found. Re-installing the application may fix this problem.
I do not get this error when using the configuration dialog in the example VIs.
Any suggestions as to the cause and/or the solution?
Thanks,
Ryan

Hello -
When you create a PDA VI that calls a DLL, you must include the .c or .lib file that corresponds to the DLL. Take a look at these documents:
LabVIEW PDA Module Build Errors with VIs that Call DLLs
Why Do I Receive Errors When Calling a C++ DLL from a Call Library Node Using the LabVIEW PDA Module...
How To Call External Code in LabVIEW PDA for Palm OS
H
ow To Call External Code in LabVIEW PDA for Pocket PC
Hope this helps!
S Vences
Applications Engineer
National Instruments

Help to make opencv's dll and LabVIEW's Call Library function node understanding each others

Hi, i have a little problem trying to use a C++ opencv's dll in labview. I wrote a really simple and stupid dll just to try to understand how it works the call library function node. Here the header code:
#ifdef GENERICDLL_EXPORTS
#define GENERICDLL_API __declspec(dllexport)
#else
#define GENERICDLL_API __declspec(dllimport)
#endif
#include "stdafx.h"
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <string.h>
#include <stdio.h>
#include <opencv/cv.h>
#include <opencv/highgui.h>
// Questa classe è esportata da Generic DLL.dll
class GENERICDLL_API CGenericDLL {
public:
int Summ(int a, int b);
int Sott(int a, int b);
int opencv(int a);
// TODO: aggiungere qui i metodi.
and here the .cpp:
// Generic DLL.cpp: definisce le funzioni esportate per l'applicazione DLL.
#include "stdafx.h"
#include "Generic DLL.h"
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <string.h>
#include <stdio.h>
#include <opencv/cv.h>
#include <opencv/highgui.h>
using namespace cv;
using namespace std;
// Esempio di variabile esportata
GENERICDLL_API int nGenericDLL=0;
// Funzioni esportate.
GENERICDLL_API int Summ(int a, int b)
return a+b;
GENERICDLL_API int Sott(int a, int b)
return a - b;
GENERICDLL_API int opencv(int a)
const string ind = "C:\\Users\\sviluppo\\Desktop\\Tuli.bmp";
const string ind_2 = "C:\\Users\\sviluppo\\Desktop\\Tuli_Gray.bmp";
//Mat image;
return 5;
i can call all the three simple functions in labview with this easy code. No problem at all. If i uncomment the line "Mat image;" the call library function node doesn't work and i receive the error:
"The library specified for this node cannot be found or cannot be loaded. Right-click the Call Library Function node and select Configure, then choose the correct library name or path."
I think that is a problem of dependencies between opencv libraries but i dont know how to manage this. Any ideas?
Thank you for yours time,
Francesco.

Hello Francesco,
I'm having exactly the same problem as you. I created a DLL that I can easily access from LabView. If I add one line and include "imgproc.hpp" (the only one I need), then LV gives me the same error you had. I read the thread Loura linked to, but I don't see how people actually take care of the dependecies (Klemen's examples did not work for me for the same reason, even though I recompiled the .cpp). Could you explain in detail what you did to make it work?
Thanks

Passing Variant to dll using call library function node

Hi,
Using LV2012
I have a dll that the following prototype:
SetTestResult(LPCTSTR Serial, int Test, int Result, VARIANT measuredValue);
How can I pass the Variant to this node when my variant can be either int or float.
I have tried "ToVariant" function but it is not sending data and gets error 1517 on LabView. For configuration parameters for variant I have used ActiveX type and datatype as activeX Variant Pointer.
So for call library function node my prototype looks like this:
int32_t SetTestResult(CStr Serial, int32_t Test, int32_t Result, VARIANT *measuredValue);
Can someone help me understanding What am I doing wrong here please?
Thank you,
Hiren
Hiren Patel

Hello Hiren,
Posting your code (even without the DLL) would definitely make it easier for people to point out potential issues. Here is an example that demonstrates passing an ActiveX variant to a DLL built in CVI, I would suggest cross-checking the way the Call Library Function Node has been configured.
Example:Transferring an ActiveX Reference Pointer to a CVI DLL
http://zone.ni.com/devzone/cda/epd/p/id/3343
Regards,
Tom L.

Call library function node in a loop

Hello All,
I am currently using a call library function node in a while loop which calls a third party dll to process and recieve some data.
My question is, if I am using this function in a while loop, what exactly happens?
Does the dll get called in each loop iteration, or does it keep the called dll loaded in memory and just pass the values to it to process data?
Also, if the answer to the above question is that it will make calls to the DLL in each iteration, how can we keep it loaded in memory always? I mean, if the DLL is a .NET application DLL, I believe the main .NET application which uses this DLL won't do multiple calls to the dll, rather it will keep it loaded in memory.
Thanks
FraggerFox!
-FraggerFox!
Certified LabVIEW Architect, Certified TestStand Developer
"What you think today is what you live tomorrow"

Hi,
the DLL will stay in memory as long as there is a program running which has not closed (unloaded) the DLL.
Doing repetitive calls to the DLL is irrelevant in this context. LV opens the DLL as soon as needed and will only unload it when there is no VI in memory which has a CLN to that DLL...
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

How to call a C pointer from call library function node

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