Resizing an array of struct inside a DLL using the memory manager
Hi all,
I dug deep inside the boards, but wasn't able to find a solution for my problem.
I'm building a dll, which does some imageprocessing and should return an array of structs to labview, with one struct for every element in the image.
As I don't know the number of elements beforehand and the limit of the number is numbers of magnitude larger then the expected one, I don't want to allocate such a huge chunk of memory prior to the dll call in labview.
In a former version I used a 2d array for the elements, where each row holds the values of every element. Here I used the NumericArrayResize-function, which worked quite well. But I have to add more sub-processes and using structs (or clusters in labview) appears to be more usefull and cleaner for me, in addition I had to cast some of the elements back and foreward a few times.
So one element-struct should hold 2 singles and 1 uint32. My question is now, how can I resize this array of struct with memory manager functions as the NumericArrayResize-functions does not suit this purpose?
(Accessing a given array of structs inside the DLL and after that reading the changed values in Labview is surprisingly easy )
Thanks in advance
Solved!
Go to Solution.
Well, I was able to solve it myself. I found this thread, where the first post of rolfk made me thinking. It appeared to me, that the numericarrayresize-function behaves very similar to the realloc-function of c. So I used the type unsigned int 8 (which is just one byte) and multiplied it by the number of bytes used by one struct, in my case 12 bytes (4+4+4) and then multiplied it by the number of structs (elements in the image) i have. Luckily it worked and the memory block was resized exactly as I wanted it to be. Important to note: do not forget to adjust the size element of the handle, otherwise Labview does not know about the changed size.
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Troy
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How to pass a struct to a DLL function and accessing it in another VI
Hi friends,
I am new to labview. I need to create a demo program in labview ,for displaying image from our own image capturing system. We have a DLL ( build in VC++) containing functions for capturing image from our system. Now I need to create a VI library for some of functions in DLL and Create a Demo program using those created subvi library . I used "Call Function node" and created some of subvi's.
Some of our DLL functions need to pass struct pointers. Our function prototype will be similar to the following function.
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Message Edited by aajjf on 04-19-2007 05:34 AMaajjf wrote:
Hi friends,
I am new to labview. I need to create a demo program in labview ,for displaying image from our own image capturing system. We have a DLL ( build in VC++) containing functions for capturing image from our system. Now I need to create a VI library for some of functions in DLL and Create a Demo program using those created subvi library . I used "Call Function node" and created some of subvi's.
Some of our DLL functions need to pass struct pointers. Our function prototype will be similar to the following function.
__declspec(dllexport) int __stdcall Initialize( unsigned char *imagebuffer,struct config *Configuration);
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unsigned short val2;
bool val3;
bool val4[3];
unsigned char val5;
unsigned char val6[3];
bool val7[26];
For passing "unsigned char *imagebuffer" I initialized array with "Numeric constant " and set the size of the array and send to the function.
The problem here is, I used this array in one of the subvi.
How can I use the returned imagebuffer array in my main demo program. How to connect the image array to subvi "Connecter Pane"
And which control can I use to display the image. The image data I get is form of 1-D Array .
The second problem is,
For passing the structure, I used "Bundle " and filled the bundle with all the datatypes as in my struct and passed to the function. Is it correct ? How to access this bundle after returned from function in another Vi. ie.) How to connect this bundle to the connter pane ?
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Message Edited by aajjf on 04-19-2007 05:34 AM
You say nothing about how your cluster looks but I'm afraid you did the standard error here and placed arrays in it. That is not what the C structure is representing for several reasons.
First fixed size arrays in C are inlined inside a structure, so are not a pointer but for the case of your val1 element three doubles.
Second although not relevant here because of above point: LabVIEW arrays are not the same as C arrays. LabVIEW uses a pointer to a pointer and has the size of the array in elements prepended to the array data. C simply uses a pointer and all the rest is the programmers sorrow. The Call Library Node does convert the top level element of variables you pass according to the type configuration of that parameter but does no conversion of internal elements at all. So passing clusters with anything like arrays or strings is always wrong unless the DLL is aware of the specific datatypes LabVIEW uses.
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Message Edited by DaVince on 10-22-2008 10:10 AM
Solved!
Go to Solution.
Attachments:
doubleArrayWeird.png 7 KB
wireUpDoubles.png 18 KBYou're right, this not directly described...
First you should read how LabVIEW stores data in memory,
then read about structure packing pragma,
and finally take a look to C/C++ preprocessor reference,
then you will get feeling how to solve this problem...
Otherwise own DLLs used in LabVIEW code pretty rarely, and Double precision also not very often...
The same trouble you may get with clusters, but here behaviour described:
"...The memory layout of a cluster depends on the platform you are running. LabVIEW may add padding between cluster elements so that those elements are aligned to certain address boundaries. Address boundaries relate to the concept of natural alignment. A piece of data is aligned on its natural boundary if the address at which it begins is a multiple of the size of the data. For example, a 4-byte integer is aligned naturally if it begins at an address which is a multiple of four. Most compilers have an upper limit on this boundary at which the restriction is relaxed. For instance, an 8-byte integer may be aligned on a 4-byte boundary. For the platforms on which LabVIEW runs, the alignment constraints are as follows:
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Message Edited by Andrey Dmitriev on 10-23-2008 03:38 PM -
How can I resize an array of strings?
I'm having a problem of not being able to use the CIN functions and therefore can't use the convenient resizing methods. I have tried to use NumericArrayResize to resize an array of strings, but it's not working correctly. Here's what I've tried most recently. I have tried many variations, so if you want to modify what I have posted, or just provide new code, please feel free.
typedef struct {
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NaveenLabVIEW stores string arrays as an array of handles to those strings. To resize an array of strings you need to declare a new string in LabVIEW's data space, resize the handle array, and add a handle to your new string. Here is an example program which does this.
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resize.zip 252 KB -
Resizeing an array of LStrHandles within Call Library Functio Node crashes SubVI.
Hello,
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LV: 8.2 Prof
Message Edited by [email protected] on 03-11-2009 12:26 PM
Solved!
Go to Solution.
Attachments:
subvi-resize-stringarray.jpg 7 KBTo be honest I'm not fully sure why that would crash but proper dealing is a lot more complicated than what you have done. The crash probably happens not in the C fucntion but on return of the function as LabVIEW tries to display the data. DSSetHandleSize() does not initialize the area it allocates additionally so there is likely garbage which LabVIEW then tries to interpret as string handles and consequently crashes.
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#else
if (p)
err = DSSetHSzClr(p, sizeof(int32));
else
p = DSNewHClr(sizeof(int32));
if (p)
(*arr)->elm[i] = p;
else
err = mFullErr;
#endif
if (!err)
err = LStrPrintf(p, "%ld", i);
(*arr)->dimSize = i;
return err;
Rolf Kalbermatter
Message Edited by rolfk on 03-11-2009 08:40 PM
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions -
Cluster array to c structure in DLL
Hello,
I have a problem which I am stuck at so I would really appreciate any help.
I have this function that i need to access in Labview.
ViStatus _VI_FUNC Ki_GetSystemInfo (ViSession instrumentHandle,
void *systemInfo);
Now the structure for systeminfo is as follows:
typedef struct _SYSTEM_INFO
char pchModelNum[MODEL_NUM_LEN];
char pchSerialNum[SERIAL_NUM_LEN];
char pchSysSoftwareVer[SOFTVER_LEN];
char pchPlatformVer[PLATVER_LEN];
char pchOpSystemVer[SYSTVER_LEN];
int bCardType[MAX_SLOTS]; // Enum slot_types
} systeminfo;
When i use the call Library Node function to access the above function what
should be mine
input and out paramteres. I tries making cluster of 5 st
rings and an array
of integers
It doesnt seem to work. Any help shall be appreciated.
PremalHi Premal,
Try to use arrays of [U8] instead of strings. Also, pay attention to INT - is OS dependent (assuming that you are using win9x/NT/2000, use [I32]). If you try with strings, be sure that the input string contains enough characters to store the result.
Hope this helps
p.s.: take a look on those articles mentioned in "cluster array to c structure in DLL" [http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=137&HOID=506500000005000000C05C0000&HTHREAD=000023744&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0] -
Pro*C: Getting array of structs from a PL/SQL procedure
I am trying to create a stored procedure that will take the results of a select query, put them into an array of structures and send the entire array of structs back to the calling function in the C program.
I currently do a select into a cursor and return each row one at a time over the network.
Any syntax suggestions would be of help.
nullI am trying to create a stored procedure that will take the results of a select query, put them into an array of structures and send the entire array of structs back to the calling function in the C program.
I currently do a select into a cursor and return each row one at a time over the network.
Any syntax suggestions would be of help.
null
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