Calling DLL in LabVIEW

[Vanisp]

Hi,

Given below is the code written in LabWindows in which accessing a Dll dynamically is done using Windows API's LoadLibrary(), GetProcAddress() and FreeLibrary(). 

I could successfully Load the library and get the procedure address using Call Library node in LabVIEW. But.......got stuck after that.

As I am not good in C/C++ coding, Request someone to really help me write the same in LabVIEW.

Kindly do the needful.

#include <z_CviFastIF.h>  // Function prototypes.
#include <cviauto.h>	  // CVI Active X definitions.
#include <formatio.h>
#include <cvirte.h>	/* Needed if linking in external compiler; harmless otherwise */
#include <ansi_c.h>
#include <windows.h>

typedef long __stdcall( *OLECREATEOBJECT)(char*);
static  HINSTANCE  Hinstlib;
static  long  gvntISystem;

long CviCreateFastObjects (void)
 {
OLECREATEOBJECT procAdd;
	pStrTempmem 	 = (char*)CA_AllocMemory(1);
	Hinstlib = LoadLibrary("FastTrio");
	if( Hinstlib != NULL)
{
		procAdd = (OLECREATEOBJECT) GetProcAddress(Hinstlib, "OLECreateObject");
		if(fRunTimeLinkSucess = (procAdd != NULL))
{
		gvntISystem = (procAdd)("FAST.IMFASTSystemInterface");
		return 0;
		}	
		else 
		return 1;
		}
	else
		{
return 1;
		}
}

[H_SH]

Hey,

"Call library function" is having both calling convention as WINAPI and C .. u can see them in function tab of "call library function"

i will just give u few primary steps to configure the "call library function"

1) press function tab --> select the library path and below that select the function name in drop down box.. select Run in UI thread and C as calling convention...

2) press Parameters tab --> specify the return type and press add a parameter in order to specify each of your input parameters.

this is few primary step to call library function then just finish and work in usual way of labview..

Hope it helps

HS

[Vanisp]

Hi HS,

I would like to thank you for the reply. 

But can you pls explain me what is done in the LabWindow code by calling the LoadLibrary() and GetProcAddress() functions?

And as to what is done after getting the procedure address (GetProcAddress) of the function exported in the Dll.

Thank you,

Regards,

S.P.Vani

[H_SH]

Hey S.P Vani,

First of all you can get better response if you post it in LabWindows forum but still i can give quick help on that ...

-> Any executable or DLL can link to a DLL only through an import library. and it is done dynamically by calling the Windows SDK LoadLibrary function..

-> GetProcAddress() gets the address of function and variable in DLL  

It will be great if you have look on MSDN website about DLL functions ..

Hope it helps

HS

[DFGray · Accepted solution]

All the information you need is in the C code.

•  OLECREATEOBJECT is typedefed right after all the #includes at the top.  It returns a long integer (typically I32 in LabVIEW, but could be I64 on a 64-bit operating system) and takes a string as input.  It uses standard window calling conventions, not C calling convention.
• LoadLibrary and GetProcAddress are used to get a pointer to the function (procAdd).  This is handled in LabVIEW by filling in the library location and function in the call library node.
• The call library node in LabVIEW must also be set to standard calling convention and the return value (I32) and parameter list (one string) must be set.
• the function is used to set gvntISystem with a constant input "FAST.IMFASTSystemInterface".  In LabVIEW, wire a string constant to the input and read the return value.
• you can implement the error checking, as well, by using the error output of the call library node.

 Good luck!

[Vanisp]

Hello,

Thanks a lot.

Pls find the attachment of the code and Kindly let me know whether it is correct or not..

Thanking you,

Regards,

Vani

[Vanisp]

Hi,

It is written in LabVIEW 8.0.

Also find the attachment of the Dll too.

Regards,

Vani

[Vanisp]

Hi,

Pls ignore the Fastdll.vi, I sent. 

CviGetFASTVersionNumber() calls the OLEGetFASTVersionNumber() by passing the parameters gvntISystem (obtained from CviCreateFastObjects()) and CStrBuffer as its input.

I have implemented the same for calling OLECREATEOBJECT and OLEGETFASTVERSIONNUMBER too in LabVIEW (which I have attached with this message). I have also attached the Dll file in previous messages.

Kindly have a look at it and let me know if it is correct or not.

Waiting for your reply.

void CviGetFASTVersionNumber (char *cString){

long status = -99;
FASTVERNUM procAdd;
char *cStrBuffer;

	cStrBuffer = (char*)CA_AllocMemory(300);
	if( Hinstlib != NULL){
		//get the procedure address
		procAdd = (FASTVERNUM) GetProcAddress(Hinstlib, "OLEGetFASTVersionNumber");
		if(fRunTimeLinkSucess = (procAdd != NULL)){ // if address success
			status = (procAdd)(gvntISystem,cStrBuffer);//call the function 	
			strcpy (cString, cStrBuffer); 
		}
	}	
	//Free memory 
	CA_FreeMemory (cStrBuffer);    
}

Regards,

Vani

[rolfk]

One recommendation (if you would use LabVIEW 8.5 or better):

Make the return value of the CreateObject function to be a pointer sized integer. As it is now you do assume 32 Bit Windows and DLL and that might bite you later on when you upgrade to a 64 Bit Windows, LabVIEw and DLL.

As to the implementation itself you make the typical LabVIEW Call Library Node starter error. The string to the second function is an output buffer. From LabVIEW you are used that it will take care to resize any string or array automatically to whatever size is needed. That does not work for DLL calls.

Did you notice the CA_AllocMemory(300) call in the CVI source code? For what might this be necessary??

Indeed it allocates a memory buffer for the function to write in the version string. LabVIEW has no way to know that this function wants a buffer to write in this information so you have to explicitedly tell LabVIEW that.

You do this with Initialize Array by creating a byte array large enough for the function parameter and then using the Byte Array To String function to turn it into the string. If you had LabVIEW 8.5 or better you could also simply configure this parameter in the Call Library Node configuration dialog to be of the desired minimum size and LabVIEW will take care about allocating that buffer automatically.

Ohh and by the way you should put a Delay function in the False case. Otherwise the loop does try to do very hard nothing and that has a rather nasty effect under LabVIEW for Windows of monopolizing the CPU almost completely.

Message Edited by rolfk on 06-03-2010 09:22 PM

[StevenA]

Vanisp,

Have you tried the "Import Shared Library Wizard".  Try it out it works good.

Tools menu >> Import >> Shared Library (.dll)...

Steve