LabVIEW
pointer to array
ivan_div wrote:
> Hello,
>
> I'm trying to find out how to define an array, and send a pointer to
> it.
> In other words: I've imported a DLL (written in C++), and one of its
> functions needs a pointer to an array as an input.
> Let's say I have the array I need... Do I have to allocate a memory
> for it, and pass the pointer to that memory location to the dll?
> I've read somewhere on this site, that the only way to work with
> pointers in LabVIEW is by using the "call library function". Is there
> any way to create an array and a pointer to it in labview without
> going through the call library functions?
Well you will have to use the Call Library function to call your DLL
function won't you? 😉 Ohh I see you created an Active X interface
for the DLL, ohh my God!
If you would call the DLL fucntion through Call Library Node instead,
LabVIEW would do all the work for you. Or have the ActiveX method take
a string or variant value instead.
> Even if that were the only way, can anybody help me to get started?
>
> In the attached VI, using "Invoke Node" I call a function named "Set
> Data". The function has 2 input variables:
>
> 1. pbyData - This is the pointer (type U8) to a buffer that contains
> the array;
> 2. wDataLength - The length of the array.
>
> What should I connect to these 2 inputs?
Create an Array of U8 integers with the Initialize Array function. Wire
that array to a Call Library Node (CLN) setup as following:
Library Name: LabVIEW
Function Name: MoveBlock
Calling convention: C decl
return value: void
1. param: source, array of U8 pass as LabVIEW array handle
2. param: target, uInt32, passed by reference
3. param: length = 4
The final array pointer (param2 output) incremented by 4 is now what you
want to pass to your ActiveX method together with the intial length of
the array.
NOTE!!: Make sure the array you intialized stays valid until after the
ActiveX method returns. This means for instance wiring the right side of
the first parameter of the CLN to a sequence frame which also somehow
depends on the ActiveX node having been executed (error cluster output
to the same frame wired) and don't branch the array wire before you
arrive in that (sequence) frame.
Rolf Kalbermatter
>
> Thank you in advance,
> Ivan
> Hello,
>
> I'm trying to find out how to define an array, and send a pointer to
> it.
> In other words: I've imported a DLL (written in C++), and one of its
> functions needs a pointer to an array as an input.
> Let's say I have the array I need... Do I have to allocate a memory
> for it, and pass the pointer to that memory location to the dll?
> I've read somewhere on this site, that the only way to work with
> pointers in LabVIEW is by using the "call library function". Is there
> any way to create an array and a pointer to it in labview without
> going through the call library functions?
Well you will have to use the Call Library function to call your DLL
function won't you? 😉 Ohh I see you created an Active X interface
for the DLL, ohh my God!
If you would call the DLL fucntion through Call Library Node instead,
LabVIEW would do all the work for you. Or have the ActiveX method take
a string or variant value instead.
> Even if that were the only way, can anybody help me to get started?
>
> In the attached VI, using "Invoke Node" I call a function named "Set
> Data". The function has 2 input variables:
>
> 1. pbyData - This is the pointer (type U8) to a buffer that contains
> the array;
> 2. wDataLength - The length of the array.
>
> What should I connect to these 2 inputs?
Create an Array of U8 integers with the Initialize Array function. Wire
that array to a Call Library Node (CLN) setup as following:
Library Name: LabVIEW
Function Name: MoveBlock
Calling convention: C decl
return value: void
1. param: source, array of U8 pass as LabVIEW array handle
2. param: target, uInt32, passed by reference
3. param: length = 4
The final array pointer (param2 output) incremented by 4 is now what you
want to pass to your ActiveX method together with the intial length of
the array.
NOTE!!: Make sure the array you intialized stays valid until after the
ActiveX method returns. This means for instance wiring the right side of
the first parameter of the CLN to a sequence frame which also somehow
depends on the ActiveX node having been executed (error cluster output
to the same frame wired) and don't branch the array wire before you
arrive in that (sequence) frame.
Rolf Kalbermatter
>
> Thank you in advance,
> Ivan
ivan_div wrote:
> Ok, let's do this the easy way... You said: "If you would call the DLL
> fucntion through Call Library Node instead,LabVIEW would do all the
> work for you."
>
> How?
>
> I'm calling the function from the DLL but it still expects a pointer
> as an input parameter (pbyData). How can I feed in a simple array of
> U8 ?
You simpy create an array of U8 with Initialize Array of the right size
and pass it to the Call Library Node parameter, which has been
configured to use Array of uInt8, 1 dimension, pass as C array pointer.
LabVIEW will take care to pass the pointer to the data part of the
LabVIEW array to the DLL and make sure that pointer stays valid as long
as the Call Library Node needs to execute.
Rolf Kalbermatter
> Ok, let's do this the easy way... You said: "If you would call the DLL
> fucntion through Call Library Node instead,LabVIEW would do all the
> work for you."
>
> How?
>
> I'm calling the function from the DLL but it still expects a pointer
> as an input parameter (pbyData). How can I feed in a simple array of
> U8 ?
You simpy create an array of U8 with Initialize Array of the right size
and pass it to the Call Library Node parameter, which has been
configured to use Array of uInt8, 1 dimension, pass as C array pointer.
LabVIEW will take care to pass the pointer to the data part of the
LabVIEW array to the DLL and make sure that pointer stays valid as long
as the Call Library Node needs to execute.
Rolf Kalbermatter
ivan_div wrote:
> I really have problems understanding you... How can I pass an array of
> U8 to the Call Library Node parameter that expects U8 number and not
> an array. I'd get a broken wire... Please be more specific or please
> send me an example code.
Hmm, I said configure the parameter as:
- Array of U8
- 1 dimension
- pass as C array pointer
I can't see where you could possibly see that I said to configure it as
an U8 integer.
Rolf Kalbermatter
> I really have problems understanding you... How can I pass an array of
> U8 to the Call Library Node parameter that expects U8 number and not
> an array. I'd get a broken wire... Please be more specific or please
> send me an example code.
Hmm, I said configure the parameter as:
- Array of U8
- 1 dimension
- pass as C array pointer
I can't see where you could possibly see that I said to configure it as
an U8 integer.
Rolf Kalbermatter
ivan_div wrote:
> I really have problems understanding you... How can I pass an array of
> U8 to the Call Library Node parameter that expects U8 number and not
> an array. I'd get a broken wire... Please be more specific or please
> send me an example code.
This is a screen shot of the relevant settings in the configuration dialog.
Rolf Kalbermatter
> I really have problems understanding you... How can I pass an array of
> U8 to the Call Library Node parameter that expects U8 number and not
> an array. I'd get a broken wire... Please be more specific or please
> send me an example code.
This is a screen shot of the relevant settings in the configuration dialog.
Rolf Kalbermatter
