Can I create a new structure within CIN?

Question

I can't create following structure using LabVIEW
typedef struct _I2C_TRANS {
BYTE byTransType;
BYTE bySlvDevAddr;
WORD wMemoryAddr;
WORD wCount;
BYTE Data[256];
} I2C_TRANS, *PI2C_TRANS;
I need this structure to a DLL-call.
I tried put all elements to a cluster, but CIN creates two separate structures (see attached) and it doesn't work. I want to know how to create one structure for a DLL call LONG _stdcall DAPI_WriteI2c(HANDLE hDevInstance, I2C_TRANS * TransI2C);
If there are any solutions for this, please let me know.
Thanks in advance
Martti Haro
Attachments:
structure.c ‏1 KB

Answer 1

"Gabriela Tillmann" wrote in message
news:[email protected]..
> Hi
> I'm afraid you'll get not by without writing a little C-wrapper to
> convert the data types.
That's not entirely true. It is possible but a little bit tricky.
typedef struct _I2C_TRANS {
BYTE byTransType;
BYTE bySlvDevAddr;
WORD wMemoryAddr;
WORD wCount;
BYTE Data[256];
} I2C_TRANS, *PI2C_TRANS;
The byte array inside the structure is fixed size and therefore each
compiler
will just embed this into the structure creating really a memory block of
1 + 1 + 2 + 2 + 256 = 262 bytes.
LabVIEW uses internally byte packing except on PA-RISC and Sparc systems
so that you need to make sure that the DLL you want to call uses also that
or if
it doesn't adjust for this too on the diagram level.
Assuming that the underlying DLL uses byte packing too, you can create a
cluster
in LabVIEW containing the first four parameters, wire it through the Byte
Swap
function and typecast it to a U8 array, append an 256 element U8 array and
configere the Call Library Node to pass this as a pointer to an U8 array. If
you
need to extract data after the call to the DLL you need to typecast it back
and/or
extract the data array accordingly. Remember that typecasting on Windows has
the effect of byte and word swapping data that is why the Byte Swap function
is
necessary.
In general it is very often possible to call DLL functions directly even if
they take
compund data types but it is a little hassle. If it is about calling a few
function the
hassle may be worth your time as starting up a C development system and
creating
a DLL project certainly has some overhead. For more involved API calls it is
usually always better to create your own wrap
per DLL, making the parameters
and function calls more LabVIEW friendly.