Return pointer dll

All,
I have an issue.
I am trying to call a function within a dll that is the following:
RtxGetPortEnumerationList()
This function is returning is either a Null pointer if devices have not been enumerated or a Non-zero pointer to a buffer allocated by the library and there are no input parameters.
The issue that i have is when creating the vi for it, i am only able to return a U32 value and do not have access to read a pointer. Why is this so?
Is there any way around it?
Thanks-N-Advance
FD
Attachments:
Call Function.JPG ‏40 KB

Accessing a windows API is pretty much the same as any api. Simply select
user32.dll or kernel32.dll (shell32, gdi32, etc), and select the desired
function. The function to use is the hard part. You can search the MSDN (ms
developers network) to see how each function works. I'd look at the lstrcpy
(in kernel32.dll) function. This function doesn't seem very sensible to use,
it copies one string to another. But in LabVIEW, you can use it to convert
the pointer (a numeric value, which points to a string) to a string (also a
pointer, but LabVIEW converts it to string). If you have an array of
strings, each string is terminated by a NULL (=0). So if you read a string,
add the string length +1 to the pointer to get the next string. Repeat
untill you get an empty string (the array is terminated by NULL NULL). It's
a hassle, but it works.
The LabVIEW API is a bit different. You don't select a dll, but LabVIEW.exe.
Executables can export functions just like dll's. The functions are not all
documented, but some are. The functions of interrest are probably one of
these: PToCStr, CToPStr, LToPStr or PToLStr. The prototypes are in the
LabVIEW directory under cintools\extcode.h.
Save your work before each run!
Regards,
Wiebe.

Similar Messages

CLN - 1-wire TMEX drivers - calling TMNext - returning pointer memory location

Summary
~~~~~~~~~~~~~~~~~~~~~~
How do I call this function from a Call Library Node?
short far pascal TMNext(
long session_handle, // session handle for the desired 1-Wire network
void far *state_buffer // state buffer provided for the 1-Wire network session
Background
~~~~~~~~~~~~~~~~~~~~~~
Hiya,
I searched the forum for 1-wire drivers, but it doesn't seem that there are any. So I thought I'd write some (if I manage it, I'll post them back here) - they'd probably be useful for someone else. They call the functions used by the TMEX 1-wire drivers http://www.maxim-ic.com/products/ibutton/software/tmex/index.cfm
I've managed to get TMExtendedStartSession and TMSetup to work (or, at least, not crash), but I'm struggling to get the TMNext function to work. The problem seems to be getting the correct settings for *state_buffer. This seems to be an array of bytes, dimensions 0 to 15360, but I get a bit baffled by pointers - I think I understand them in principle, but in practice, I usually end up in a bit of a mess!
How to configure?
Numeric or Array? Or adapt to type?
Pointer to Value, Array Data Pointer, etc?
Do I need to dimension a Labview array to 15360 (or 15361) and pass it to the CLN to get the correct array back?
Here is a C example from the support documentation , or I've got a VB example if you'd prefer.
long session_handle;
unsigned char state_buffer[15360];
short result, cnt = 0;
/* session_handle set from a call to TMExtendedStartSession */
/* attempt to find the first device on 1-Wire network */
result = TMFirst(session_handle, state_buffer);
/* loop to count all of the devices on the 1-Wire network */
while (result > 0)
   cnt++;
   /* find next device */
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/* close the session with a call to TMEndSession */
I'd be very grateful for advice on this - I think if I can get this cracked then CLNs will no longer be the scariest icon on the Labview functions palette.
Many Thanks
Joolz

Hi,
if I'm understanding this correctly, the state buffer is an array of U8's that gets filled in by this function.
You need to do an initialise array of the U8 type of the appropriate size, and then pass this into the dll at the appropriate parameter.
See the following example code item for a better explanation :
http://venus.ni.com/stage/we/niepd_web_display.DISPLAY_EPD4?p_answer=&p_guid=C9914D5A718C627EE034080...
This should work for you, but failing that, you could always wrap it's functionality with a c-based environment, and pass the values to that from LabVIEW< using it as a means of performing the conversion.
Hope that helps
Sacha Emery
National Instruments (UK)
// it takes almost no time to rate an answer

Return points within certain distance to each other

I have a geometry of points (say 1000 points) and I want to return only points within certain distance(say 100 meters) to each other and exclude others. I have been using the sdo_aggr_union with tolerance value of 100, but it returns one of the points from all of which are 100 meters apart and also returns other points.
I would appreciate if anyone can please help me with this. I basically want to identify bunch of points placed close to each other. sdo_within_distance will not work as this is between two geometries. Here I have the same geometry column in the table but multiple records. Sorry, if I have confused too much.Thanks in advance.

Hi
Your initial question said you want to find all points within a certain distance to the each others. The distance was said to be 100 meter.
Therefor the query will return for every single point all the others that are within that distance.
As this is performed on one single table the SDO_JOIN is well suited.
Obviously this returns a lot of recs. Let me explain why. draw for example 5 points (on a line to make it simple) and every point is 10 meters further from the previous. If you want to know for the first point what are the others within the 100 meter distance, you will end up with all the others. So doing this for every point this means that for every point you will have returned all the other, increasing the number of records returned. this is actually what the example query will do.
If you have additional filters you must add them for both (in your case same) tables, if you want for all points with a specific faceid to list all other points within that distance and with the same faceid.
However this will not be limited to only 549 recs I expect.
Maybe you can try to give more explanation what you are trying to achieve.
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tx
Luc

Should a method have only one return point/statement?

Hi,
sometimes I have Code that looks like
public boolean equals(final Object o) {
    if (o == null) {
      return false;
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      return true;
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}Is it best practice to use return in this manner? Some code metric tools report this use of return as bad coding practice.
What are the pros and cons of the short return?
Thanks for your answers

tmnelson wrote:
So we should pervert exception handling by putting all our code into try/finally blocks? I don't think that's gonna fly...That doesn't make much sense to me and I don't know what it has to do with what I said. One of the good reasons for forcing a single return is that you can put all the required cleanup code at the end of the method. Finally blocks accomplish this same end. This is not a perversion. In fact, finally blocks are superior in this regard because they are guaranteed to execute, even if the method doesn't complete normally. Single return cannot make this guarantee.
Um, I still only see one return. Only now it's in the wrong place. Why not just add the appropriate else clause to the original code? That's what you're going to wind up doing in your "improved" code, anyway.You seem to have completely missed the point. Both code snippets are wrong. My improved version doesn't compile. It's impossible to miss. The other version was deployed into production. In my experience a compilation error is a much better problem to have than a production system crash.
I don't see any value in forcing the single return. Actually I think it generally makes code much harder to read. It turns the execution path from a tree into an onion.I think it's a good rule of thumb, up there with placing braces after your if statement and documenting when a case statement falls through. It was more important when people wrote 100+line functions, as it was mighty confusing to place a breakpoint at some line and then never hit it because the code executed a return twenty or so lines before your breakpoint. This is still a potential problem today, but people tend to write shorter routines, so it's less common.It's a rule of thumb that makes sense in languages without the high-level control structures that Java has. COBOL is an example of such a language where forcing single returns is really important but it doesn't have a true method structure. It doesn't make sense in Java. And for long methods, the proper advice is to shorten them, not to force a single return.
ISTR that compilers could perform certain register optimizations if routines only had one entry and exit point, but I can't find a definite reference, and that may have only been valid for block-structured programs anyway. Or loops.This is complete nonsense. The compiler or JVM can optimize your code much better than anything like this will accomplish. There's no reason that the JVM can't treat a method with multiple return statements as having a single return statement given that all paths are guaranteed to return a value of a specific type or an exception will be thrown.
If you just declare the variable and don't assign it, the compiler will complain if there is a path that doesn't guarantee that it is assigned before it is used.This doesn't work in many IDEs, as the editor won't perform much static analysis, it'll just flag the declaration as an error and refuse to compile the code until you "fix" it.I didn't mention IDEs. This is part of the Java Language Specification. No compliant compiler will allow such code to be compiled.

Structure pointer dll

Need some help here, as I have tried everything I can think of.
Created a cluster, representing the structure and in die call function I have set 'Adapt to Type' and array data pointer, but this keeps failing as you can see below
Will appreciate any help/advise to get this working...
Solved!
Go to Solution.

You add strings to the cluster. They will be passed to the DLL as LabVIEW string handles, something only DLLs can handle that have been specifically written to work with LabVIEW datatypes.
The real solution depends on how your structure is defined in C. If it contains fixed size string arrays, you have to replace that with a LabVIEW cluster with as many U8 or U16 integers as your fixed size string is defined. If they are defined as string pointers you have to place an uInt32 (for 32 bit LabVIEW) or an uInt64 (for 64 bit LabVIEW) for each string pointer and do some pretty convoluted memory management on your own (which you also would have to do if you used that function from a C program).
Your structure is however defined to contain fixed size arrays so the first solution is applicable.
You also need to check your structure again. aIPAddr is a cluster of 16*U8 elements and abMACAddr is a cluster of 6*U8 elements, not a single U8 element. Time is an int which is a signed integer that translates in LabVIEW to an int32. IsDHCPAssignedIP up to NumIPConnectionsIsValid are single char elements not a string and therefore translate to a single uInt8 in LabVIEW. And finally aPadding is again a cluster of 34*U8 not a single U8.
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

How to fix Entry Point dll error?

Premiere Elements has been running OK for a couple of years, had to replace C drive. After reloading Premiere Elements 4 I get the following error (Vista).
?resolveEntity@DefaultHandler@xercesc_2_2@@UAEPAVInputSource@2QBG0@Z could not be loaced in the dynamic link library xerces-c_2_7.dll
Thanks

BTW, when you replaced your C drive, you didn't just make a copy of the disc's files and copy them to the new drive, did you?
This often doesn't work. It's a much better idea to re-install your software after you've installed the operating system. Otherwise, problems like you're describing are pretty common.

Pass char array to c++ DLL and return same char array

Lectori Salutem,
Here is the situation:
Im learning TestStand, and to learn the basics, I want to do the following:
Call a (C++) DLL in TestStand with an array of chars.
The DLL should return the array of chars (or a pointer to the datalocation).
This is the code in my DLL:
TESTDLL3_API char* bounceString(char data[])
data = "Hello World";
cout << data;
char* pointer = data;
return pointer;
However, this function will not be recognized by TestStand
When this is working, I think I can build the rest of the functionality by myself.
Thanks in advance for any help!
Jeroen
The Netherlands
Solved!
Go to Solution.

Sadly, in the example there is no return value to TestStand.
However, I did manage to return the pointer of the char array to TestStand:
int __declspec( dllexport ) bounceString2(char* argument)
void *pointer;
int i;
argument = "Hello";
pointer = argument;
i = (int) pointer;
return i;
So, right now I have to find out how to retrieve the char array from the pointer...
Jeroen
PS, I will look at the CVI code, and let you know about my process

Dll in lv7

Use the CALL LIBRARY FUNCTION to access a function in a DLL
Attachments:
DLLQuestion.txt ‏1 KB

There is one of two ways.
First write or modify the function to be more "LabVIEW friendly" LabVIEW can pass you a pointer to a c string and the function can fill in the body(be careful to allocate space in the labview string before calling) but it can not move memory for you. For a pointer to a pointer or a returned pointer, either your routine must do the moving or if the memory pointed to is static, you can call a windows DLL function to move the memory into labview space. It may be most straight forward if you write a "helper" routine (first option)
Stu McFarlane
Viewpoint Systems, Inc.

Pointer to LabVIEW Array

LabVIEW memory management question:
Question Part 1: When I write a C .dll that takes a LabVIEW array,
LabVIEW passes a pointer into LabVIEW's memory to the array to C.
Can C return the pointer to me (e.g., not the array I passed in, but
it's memory location)?
i.e.: void GetNativeMemoryPointer(float *pointer, float *array);
where *array is my input array, and GetNativeMemoryPointer returns the pointer to this array on *pointer.
Question Part 2: What issues will I run in to if I pass this returned
pointer to another .dll call. What if this .dll call is in
.NET?
Concerns: How does LabVIEW hold this array in memory? When I call
GetNativeMemoryPointer, does LabVIEW make a copy and send this a
pointer to the copy to the dll, or is the pointer to the
original? Will LabVIEW ever "move" the original, e.g., will my
pointer become invalid after some time?
Joe Gerhardstein
Averna Test Systems
Certified LabVIEW Architect
http://www.averna.com

Part 1: I must confess that I don't understand your question. Pointers and arrays are very closely related in C so I'm not following the sequence. So I don't know if the following applies, but here is a possible answer...
The pointer to a LV array that is passed to a call library node is valid ONLY during that call. Once the call to the DLL completes, you should consider that pointer value invalid. You can, of course, make a copy of the array and return a pointer to your copy - but LV won't know what it is. It definately won't show up in LV as an array. However, you can pass that pointer to the copy around to other DLLs as much as you want.
* Don't forget to free the copy. If you make a copy of the array, you own it - therefore you must free the memory of the copy at some point *
Part 2: Easier to answer.
* If you want LV to convert your pointer to a LV data type (such as a LV array): Take a look at page 2-4 in the "Using External Code in LabVIEW". In almost all cases we do not support pointers. The only exceptions are the ones shown in the Call Library Node configuration. For arrays, notice that if you want to return an array to LV, we have our own defined data types for this - read up on the CIN section for more information.
* If you want to return a pointer than LV just messages to other DLLs: No problem. Put the parameter to the routine as a pointer to integer (or a return value of type int). Thus your pointer is an integer as far as LV is concerned. When you pass it to another DLL, we'll pass the exact same value to the DLL - thus the pointer is never modified or the data touched.
Did this help?
Message Edited by Lycangeek on 08-10-2005 02:12 PM
Brian Tyler
http://detritus.blogs.com/lycangeek

Pbm in Dll (pls Francois)

Hi,
I created a test.dll using Microsoft visual c++ by following steps.
I opened a new project by
New--Project--win32 dynamic link library
I added a new src file test.c to project and edited it as:
int caps()
int *src=0x417;
if (*src==64)
return 1;
else
return 0;
I added a header file test.h and added
int caps()
I compiled the test.c with no errors.Then I built test.dll by pressing make test.dll.
Now If I view test.dll with a utility called DLLEXP(Utility to see func present in DLL),
Caps is not appearing in it.Thats y forms is also giving an error like caps is not found in test.dll.
I'm totally confused.
What is wrong in my process?
Pls its urgent...I've to use this dll in ORA_FFI package.
Adios..

Here is a Metalink sample
The memory for the char pointer must be globally allocated using a GlobalAlloc
(with the GMEM_FIXED flag) such that the memory is not resident on the stack.
The problem with allocating memory on the stack for the pointer is that this
memory block will be freed when the function exits and the returned pointer
will become invalid.
Here is a complete example showing a successful implementation of this
functionality. Although the following code demonstrates a 16bit
implementation, the same holds true for 32bit implementations.
-- This calling trigger's code                                --
declare
-- Parameters
parm1 VARCHAR2(128) := 'X';
-- Return value
rt VARCHAR2(512) := 'Hello Folks';
begin
rt := MyLib.MyFunc1( parm1 );
Message(rt);
end;
-- This wrapper package's header                             --
PACKAGE MyLib IS
FUNCTION MyFunc1( parm1 IN OUT VARCHAR2 )
                    RETURN VARCHAR2;
END;
-- This wrapper package's body                               --
PACKAGE BODY MyLib IS
lib_hndl ora_ffi.libHandleType;
func_hndl ora_ffi.funcHandleType;
FUNCTION i_MyFunc1( func_hndl IN ora_ffi.funcHandleType,
                      parm1 IN OUT VARCHAR2 )
                      RETURN VARCHAR2;
PRAGMA INTERFACE(C,i_MyFunc1,11265);
FUNCTION MyFunc1( parm1 IN OUT VARCHAR2 )
                      RETURN VARCHAR2
IS
    parm1_l VARCHAR2 := parm1;
    rc       VARCHAR2(512);
BEGIN
    rc := i_MyFunc1(func_hndl, parm1_l);
    RETURN (rc);
END ;
BEGIN
lib_hndl := ora_ffi.load_library(NULL,'DLL16.DLL');
func_hndl :=
ora_ffi.register_function(lib_hndl,'PASCAL_TEST',ora_ffi.PASCAL_STD);
ora_ffi.register_parameter(func_hndl,ORA_FFI.C_CHAR_PTR);
ora_ffi.register_return(func_hndl,ORA_FFI.C_CHAR_PTR);
END;
-- This DLL's DEF file                                       --
LIBRARY      DLL16
EXETYPE      WINDOWS
CODE         PRELOAD MOVEABLE DISCARDABLE
DATA         PRELOAD SINGLE
HEAPSIZE     4096
EXPORTS
             WEP PRIVATE
             Pascal_Test @1
-- This DLL's CPP file                                       --
#include <windows.h>
#include <string.h>
int CALLBACK LibMain(HANDLE hInstance, WORD wDataSeg, WORD wHeapSize, LPSTR
lpszCmdLine)
        if (wHeapSize > 0 )
                UnlockData (0); // Unlocks the library's data segment
        return 1;
char* FAR PASCAL __export Pascal_Test (char* xyz)
    HGLOBAL hgl;
    char FAR* abc;
    hgl = GlobalAlloc(GPTR, 256);
    abc = (char*)GlobalLock(hgl);
    strcpy(abc,"Hello World");
        GlobalUnlock(hgl);
        MessageBox(NULL,abc,"Pascal",MB_OK);
    return abc;
}Hope this help
Francois

IMAQ GetImagePixelPtr Unmap Pixel Pointer - do I really need this?

Hi!
What exactly does IMAQ GetImagePixelPtr with Unmap Pixel Pointer function? The Help says "Frees the pointer and related information previously obtained using Map Pixel Pointer." OK, Map Pixel Pointer will return pointer to pixel (0,0). But after Unmap this pointer still valid... Why we needed Unmap Pixel Pointer?
In general there are two questions:
1. What may happened theoretically if I will forgot Unmap Pixel Pointer after Map Pixel Pointer?
2. Do I need to call Map/Unmap pixel pointer if I working with images directly in my DLLs?
thank you in advance,
Andrey.

Hi, Greg,
Thank you for the answer. Let me explain my question.
When I need to make some calculation inside of the DLL, then recommended way looks like this (got it from NI Help):
According C code should be:
I don't like such method, because for each image I must transfer to the DLL: pointer, width, height, linewidth, etc.
I prefer more simple way:
Now I will obtain all image parameters inside of my DLL code, and I have only single argument instead of multiple:
But now I'm not sure - probably I must "isolate" direct usage of the pointer (imageStart member of the ImageInfo) with Map/Unmap calls? Probably MapPixelPointer will "lock" pointer and will prevent relocation of the image in the memory in LabVIEW during LLB call, or something like this... Or given code is safe? This is why I'm asking about detailed explanation of UnMap function.
with best regards,
Andrey.

Reading exported variables from DLL

Dear Community,
I am trying to read a variable that is exported by a third-party DLL inside a LabView VI. If it were a function, then I would just use a "Call Library Function" subvi. But it's not a function; it's a variable, something like
__declspec( dllexport ) int foo;
as opposed to
__declspec( dllexport ) int foo();
Is there something like a "Read Library Variable" vi?
Thanks,
Cas

cwierzynski wrote:
> Dear Community,
>
> I am trying to read a variable that is exported by a third-party DLL
> inside a LabView VI. If it were a function, then I would just use a
> "Call Library Function" subvi. But it's not a function; it's a
> variable, something like
>
> __declspec( dllexport ) int foo;
>
> as opposed to
>
> __declspec( dllexport ) int foo();
>
> Is there something like a "Read Library Variable" vi?
Nope! Although possible in Win32 DLLs (Win 3.1 had no standard form for
exported variables at all) it is very seldom used and in fact a bad idea
to do so. Notice that even some normal compilers are not able to
generate the correct export or import mechanisme for them. You could
write a wrapper DLL which exports a read and write function
to those
variables.
I guess with some magic voodoo it would be even possible to generate
some VI code to load the symbol with LoadLibrary and GetProcAddress and
reference the returned pointer as pointer to the variable. Still writing
a wrapper DLL is more secure and IMO the proper way to go.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

How to return more than one value from a function

hello everybody,
Can anyone tell me how to return more than a single value from a function, the problem is i have 4 points,
2 points form one line ,another 2 points form 2nd line ,each point is 3 dimensional(x,y,z coorinates) so i will pass these values to func(x1,y1,z1,x2,y2,z2,x3,y3,z3,x4,y4,z4), i will find the point of intersecton of two lines and i will get it as x,y,z , now how to return these 3 coordinates,usually the function returns only one value, please help me to solve it out.
Thanks.

I think the easiest way or trick here is (easiest isn't always the best as we know, but atleast this one will work) to create simple data array. and pass that. Create an array with:
<code>
class justArray {
int x=0
int y=0;
int z= 0;
...somewhere
justArray[] points= new justArray[4];
points[0].x= ..
points[0].y= ..
points[0].z= ..
points[1].x= ..
return points[]
</code>

Import message table from DLL

Is there any way to import a the message table resource from a DLL (or, specifically, an OCX file) into LabView such that the error dialogs will properly report error codes returned by DLL calls?
Thanks!
Solved!
Go to Solution.

Yup, that was the fallback plan. I noticed that there's a provision for user-defined codes and messages and would have generated a message .txt file, but the DLL message codes don't fit in the LabView's user code ranges. So fn call it is.

Point-in-polygon query with SDO_GEOMETRY.RELATE

Hello All,
I'm trying to perform a simple point-in-polygon query using
SDO_GEOMETRY.RELATE. Only the "anyinteract" mask seems to return
the correct answer. Can someone point out what I'm doing wrong
and/or suggest a better way to do this. My objective is simply
to return a count of the number of features in the point table
that fall with the selected feature in the polygon table.
select count(*) count from pnttest pnt, polytest poly,
user_sdo_geom_metadata m where SDO_GEOM.RELATE(pnt.shape,
m.diminfo, 'anyinteract',poly.shape,m.diminfo) = 'TRUE'
and m.table_name = 'POLYTEST' and m.column_name = 'SHAPE' and
poly.ADMIN_NAME = 'California'
I would have thought the "inside" mask would be what I want but
it returns 0 instead of the correct answer of 6.
Thanks for any help or suggestions!
-- john

Hi John,
If I wanted to do this as fast as possible, and didn't mind
returning points that touch the boundary of the polygon, I would
do something like this (assuming the point layer is indexed):
select /*+ ordered */count(*) count
from polytest poly, pnttest pnt
where SDO_RELATE(pnt.shape,poly.shape,
'mask=anyinteract querytype=window') = 'TRUE'
and poly.ADMIN_NAME = 'California';
If you are wondering what relationship Oracle Spatial thinks
there is between the 6 points and the state, try using the
determine mask with the 6 geometries that return from
anyinteract.
If you are using Oracle Spatial pre-9i, you might also want to
add layer_gtype=point in the quotes.
Hope this is useful.
dan

Return pointer dll

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