The LV crashed when I call a dll to control my com port

Question

I am controlling the com port with calling a dll(dwdio.dll--see the attachment). The VI I used is also attached below.
I just used four functions of this dwdio.dll, as followings:
1. bool DWD_set_comport(unsigned char com_port,int *handle)
Parameter config:return type--unsigned 8-bit int(value),com_port --unsigned 8-bit int(value),handle--signed 32-bit int(point to value)
bool DWD_set_baud_rate(int baud,int *handle)
Parameter config:return type--unsigned 8-bit int(value),baud--signed 32-bit int(value),handle--signed 32-bit int(value)
bool DWD_check_comm_link(int *handle)
Parameter config:return type--unsigned 8-bit int(value),handle--signed 32-bit int(value)
bool DWD_close_com_port(int *handle)
Parameter config:return type--unsigned 8-bit int(value),handle--signed 32-bit int(value)
I can run my vi successfully,but Labview will crashed when I close Labview application. I tried many ways to change the parameters and convention, but there is no effect.
Because this dll file need hardware dongle,so I can't upload the vi. I just attached the screen-shot of it.
Can anybody have some analysis on my vi to give me some valuable suggestion?
Attachments:
dwdio & explanation &my vi.zip ‏2456 KB

Answer 1

Yaoming wrote:
> SVences,<br><br>I know that Erroneous data types assignments can cause crashes.
> I have checked all the data type with my experience and knowledge,but I didn't
> find anything should cause this crash problem.<br><br>After all,I am not very
> experienced in Call Library Function, so maybe my vi still have some erroneous
> data type assignments. Can any DLL expert help me to locate them?
> For the original function description, I have posted as attachment in the first
> post. Therefore,anybody who want to check my data type error can have a check
> with that function description.
> That issue is very urgent and important to me. Can anybody to help me sort
> this problem as soon as possible? Thanks in advance.
A few remarks:
1) the Bool return value is probably an int. It doesn't look like a
standard Widnows datatype so you will have to look in the documentation.
However this is unlikely to crash your code.
2) The handle parameter for DWD_set_comport should be set as Pass:
Pointer to Value. All other parameters should be passed by Value only as
they are not pointers at all. Also please wire a 0 constant to the right
side of the CLN for that parameter to provide memory for the DLL to
write in.
3) The calling convention for the DLL functions is not obvious from your
documentation. You have the choice between C (cdecl) and WINAPI
(stdcall) on Windows. Since this DLL seems to be available for multiple
platforms (The remark for each function) it may be that the developer
decided to use cdecl calling convention (a smart choice I would say) but
Windows DLLs usually use stdcall instead.
Having the wrong one will absolutely crash LabVIEW but usually at the
moment you return from the functioncall and not later on.
So I would guess the most probable cause is number 2, but don't discount
the other ones completely.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions