Interface dll function with struct in LabVIEW

[WG-]

Hello,

I have a function:

HPDF_SetInfoDateAttr  (HPDF_Doc pdf, HPDF_InfoType type, HPDF_Date value) 

The problem is in the last input, HPDF_Date value. HPDF_Date is a struct which looks as followed:

typedef  struct  _HPDF_Date {

    HPDF_INT    year;

    HPDF_INT    month;

    HPDF_INT    day;

    HPDF_INT    hour;

    HPDF_INT    minutes;

    HPDF_INT    seconds;

    char        ind;

    HPDF_INT    off_hour;

    HPDF_INT    off_minutes;

} HPDF_Date;

Now I created the following cluster in LabVIEW:

In the Call Library VI I set the type to "Adapt to type" and tried the dataformats. However none of them worked. Can any one explain to me why the cluster is not accepted by the function? I know the error is there because the error function of the dll says that I input an invalid datetime format.

The datetime format may look like this:

Member	Effective values
year
month	Between 1 and 12.
day	Between 1 and 28, 29, 30, or 31. (Depends on the month.)
hour	0 to 23
minutes	0 to 59
seconds	0 to 59
ind	Relationship of local time to Universal Time (" ", +, −, or Z).
off_hour	If "ind" is not space, 0 to 23 is valid. Otherwise, ignored.
off_minutes	If "ind" is not space, 0 to 59 is valid. Otherwise, ignored.

[WG-]

ps. HPDF_INT is just signed int so a 32bit signed integer.

[WG-]

No one?

Well I uploaded a example. Before running you need to set the path right from where it fetches the .dll in the Call Library VI

Hope someone can help.

[majoris]

Do you have the source headers of the DLLs you are using and have you tried using the Import Shared Library function?

Also, right click on your Library Node and generate the corresponding c file. Check to see if there are any differences between the c file generated and your headers. In this way, you can go about fixing your clusters to make sure they map to the structs properly.

[WG-]

Yes I have the source of the dll and I didn't try that function, Import Shared Library, I didn't knew it excisted. I just tried and I need to give a header file... But my dll exists out of multiply of h. files and c. files. How do I know which one to choose?

I will gonne try the second part of your answer now.

I'll keep you updated.

[nathand]

EDITED:  I'm not sure you can pass a struct by value in LabVIEW.

Part of the problem is that you've replaced what should be a "char" in the structure with a string.  Try making "ind" a U8 integer instead.  In LabVIEW, you can convert that to a string by running it through build array, then using Byte Array to String.  To go the other direction, do the reverse - use String to Byte Array, then index element 0.  You might be able to use typecast instead.

[nathand]

Sorry for my slightly confused earlier message; I replied too quickly.  LabVIEW cannot pass a struct to a DLL function by value.  You'll need to write a wrapper function in C that takes a pointer to the appropriate structure, dereferences the pointer, and passes that to the library.

My initial comment about the difference between a char and a string still applies.  If you do write a wrapper as suggested above, you'll want the "ind" parameter to be a U8 as I suggested, not a string.  Also, depending on your compiler setting and how the library was compiled, you may need to add padding bytes after the "ind" parameter to align "off hours" and "off minutes" properly.

[rolfk]

Actually LabVIEW can. A struct passed by value is simply pushed element for element onto the stack. So instead of defining a structure to pass as a single parameter to the CLN, you configure the CLN to take one parameter per structure element (and use the right datatype of course).

[WG-]

Question Rofl. What do you mean with CLN?

And I tried the workaround with a U8 but wasn't succesfull. Furthermore there is really no solution to get this working? I mean this isn't even a very complicated struct.. 😕

[rolfk]

CLN = Call Library Node.

U8 is correct so stay with that. But you will have to configure one CLN Parameter per Cluster element.