LabVIEW
Need advice on setting Call Library Function Parameters
No, it's not obvious 🙂 I will try to build an example in some 5, 6 hours because currently I'm a little busy and I will send it to you 🙂
Ok, there are many trouble and difficulties with trying to do this!!
1) A Windows HANDLE is really a pointer sized integer value. So make sure to use that. Otherwise you will get into trouble when you ever try to run the code in 64 Bit LabVIEW.
2) GetStdHandle() is a nice idea to get a handle to the standard output, but it doesn't work. LabVIEW is a GUI application and as such does not initialize a console and therefore doesn't end up having standard IO handles. And the function in question does require a console handle, not a standard IO handle. A console would contain several standard IO handles, but as already said, LabVIEW as a normal Windows GUI application does not initialize a console on startup.
3) Assuming you got a valid console handle from somewhere, calling the function GetConsoleScreenBufferInfo() is not a trivial exercise. The parameter lpConsoleScreenBufferInfo is a C structure, somewhat similar to a LabVIEW cluster. In this case it does not contain any pointers so it is relatively easy to do in LabVIEW with a cluster. The magic is to read the C specification for that structure and map it exactly into a LabVIEW structure.
typedef struct _CONSOLE_SCREEN_BUFFER_INFO { COORD dwSize; COORD dwCursorPosition; WORD wAttributes; SMALL_RECT srWindow; COORD dwMaximumWindowSize; } CONSOLE_SCREEN_BUFFER_INFO;
First you have two COORD which is another cluster with two SHORT each. A SHORT is equivalent to a LabVIEW 16-bit integer. Then you have a WORD which is a LabVIEW unsigned 16-bit integer. Then a SMALL_RECT which is a structure with 4 SHORTs and last but not least another COORD.
Create a LabVIEW cluster with the embedded clusters for the COORD and SMALL_RECT, then configure the according function parameter in the Call Library Node to "Adapt to Type" and connect a constant of this cluster to the left side of that parameter and wire an indicator to the right side.
Alternatively since all the basic types in the structure are 16 bit integers you could just define the parameter as C Pointer to a 16 bit integer array. BUT in that case you have to make sure that you pass in an array which is allocated big enough so that the function can write its data into it. In this case you have to allocate an array of at least 11 16-bit integers on the diagram before passing that array to the function. Unlike in LabVIEW where a function usually allocates any array data at the moment it requires it, this doesn't work on the DLL interface like this. If a function expects a buffer to write data into (an array, a structure, or even a scalar passed as a pointer) the caller has to make sure that he passes a big enough memory buffer to the function that it can write into!!
Hi!
Rolfk, of course you are right, I was hoping it may be easier that it seems, but when I've started digging into this functions on MSDN I see it's not so straightforward.
What about, let's say workaround?
I know it is not perfect, but in some cases it may be enough to read the file - it should be possible to open the file in read mode even if there is continuous writing ongoing. Just an idea.
Marcin
