How can i create a NULL-Pointer

[OnlyOne]

Hello,
how can i create a NULL-pointer (like in C) to call a DLL-function in Labview 8?

I have this function:
XXXXXX FuncName(int32 handle,
char * aCharName,
void * aVoidName,
int32 aInt32Name,
char * Msg);

and have to call it like this:
rc=InitCasRunF(&handle, NULL, NULL, NULL, msg);

When running the vi i get a popup with this message:

Labview: An exception occured within the external code called by a Call Library Function Node.
This might have corrupted Labview´s memory. Save any work to a new location and restart Labview.
VI "......." was stopped at Call Library Function Node Call Library FuncName 0x13E0 of subVI.
Democall.vi


The attached democall.vi is not the original but its like that.

Thanks for any help how i have to create thi NULL-pointer

Message Edited by NewOne on 01-25-2006 03:42 AM

[pincpanter]

Pass null unsigned or signed 32-bit integers by value.

Paolo

[OnlyOne]

Thats what i did in my example.
Do you think this works also for a char or void NULL-pointer?

[pincpanter]

Sure, any pointer is a 32 bit value (in Win32, of course).
I don't have LV8 so I could not open your vi.
The reason for the crash should be another, in my opinion.

Paolo

[OnlyOne]

Ok, i resaved it for 7.1 perhaps you see an problem.
its not executable, just to show how i try to do it.
thx for your help

[pincpanter]

You are passing a LV null string for the second parameter. I think that LV does not pass a null pointer, rather a valid pointer to a null string.
Try replacing second parameter with a numeric one like third and fourth.
Other possibility: msg returned is longer than 255 chars.

Paolo

[OnlyOne]

Thanks for your ideas but doesnt work both.
- i replaced the string with numeric
- and tried a longer string for msg

[pincpanter]

Only few ideas remained: are you sure about the calling conventions?
Is the function working when called by a C program? Did you write the dll or inherited it or it's a system dll?

Paolo

[tbob]

Another thing to try is to change the calling convention from WinAPI to C.  Some DLLs written in C need to be called with the C calling convention.

[OnlyOne]

Thx for your help. Meanwhile it works. It was a stupid, easy thing i didnt see all the time.
I had to change the first parameter as--> Pass: "Pointer to value" instead of "Value". Thats all.
All NULL-values are passed as Int32-value.

One new problem occurs now: After runnning the function Labview crashes down.
Error-report is attached if someone can read someting in this.

When running the dll-function in a c-program it works
When calling the dll-function it in teststand it also works.

Message Edited by NewOne on 01-26-2006 05:14 AM