C library function call - Unavailable Type for one of the parameters in the Function Prototype.

Question

Hi,
I'm doing a job that has been already done by some others: implementing a LabVIEW SQLite Wrapper, I know how to do that with .NET alas I would like to do that in C, mostly for performance purposes and my poor pointer knowledge is kinda make me stuck.
A couple of informations are kindly provided here:
http://www.sqlite.org
http://www.sqlite.org/cintro.html
What I would like to do, is just to open a connection to a SQLite Database (if not existing, the SQLite engine will create the embedded Database and the related file to save the data and everything). The function to perform the operation is given in page below:
http://www.sqlite.org/c3ref/open.html
It seems pretty simple:
int sqlite3_open(
const char *filename, /* Database filename (UTF-8) */
sqlite3 **ppDb /* OUT: SQLite db handle */
int sqlite3_open16(
const void *filename, /* Database filename (UTF-16) */
sqlite3 **ppDb /* OUT: SQLite db handle */
int sqlite3_open_v2(
const char *filename, /* Database filename (UTF-8) */
sqlite3 **ppDb, /* OUT: SQLite db handle */
int flags, /* Flags */
const char *zVfs /* Name of VFS module to use */
However I'm struggling a bit about the following type:
sqlite3 **ppDb /* OUT: SQLite db handle */
And I'm not really sure about which type to use when I'm calling this function from LabVIEW
Any idea, I guess it's real easy, but I'm not really used to have a type which is I suppose the DataInstance but as it's not clearly explicted in the LabVIEW interpreted C Library Function prototype (InstanceDataType makes sense but not sure though) I'm not really sure what I'm showing in the attached screenshot is valid or not.
My VI seems to work like a charm, but don't really know if I'm doing something wrong.
Another prototype that I have no idea about the proper LabVIEW call is the close function:
http://www.sqlite.org/c3ref/close.html
Let me get this traight, usually a parameter has a name, right? but seems that nope:
int sqlite3_close(sqlite3*);
int sqlite3_close_v2(sqlite3*);
So also no idea about the parameter setting for this one... has to be considered as the self instance like the one calling this function is this... but I'm not passing any object?
Really confusing...
sqlite3*
I might sound really silly, but if anybody could point me some directions, I would be really grateful for that.
Thanks
 

Answer 1

Ehouarn wrote:
However I'm struggling a bit about the following type:
sqlite3 **ppDb /* OUT: SQLite db handle */
And I'm not really sure about which type to use when I'm calling this function from LabVIEW
This parameter should be a pointer-sized integer, passed by pointer. Doesn't matter if it's signed or unsigned. The SQLite library will allocate memory for you, then put a pointer to that memory location into the pointer-sized integer that you pass in.
As for the close function, you should pass that same pointer-sized integer, but this time pass it by value (because it's referenced with a single *, not two). There's nothing wrong with the documentation omitting the parameter name. For the purposes of a function prototype, the parameter name is unimportant, since all you need to know is the type of the data. How the function chooses to refer to that parameter internally is irrelevant.