STRUCT?

[Walt Decker]

Given:


STRUCT tPtr, _
 A$ AS PTR

B$ = "this is a test"
tPtr.A$.struct = B$

PRINT tPtr.A$.struct

to what is tPtr.A$.struct pointing?

[Carl Gundel]

May 11, 2021 17:35:15 GMT -5 Walt Decker said:

Given:


STRUCT tPtr, _
 A$ AS PTR

B$ = "this is a test"
tPtr.A$.struct = B$

PRINT tPtr.A$.struct

to what is tPtr.A$.struct pointing?

At that moment it is pointing to the string in B$, but when you use the struct in a CALLDLL the struct will be copied into non BASIC memory along with the contents of B$.  Then when the call returns the copying happens in reverse.  This sort of thing is pretty common in high level languages that have external function interfaces to C style APIs.

[Walt Decker]

How does one embed structures?

Example:

STRUCT tPnt, _
 X  AS LONG, _
 Y  AS LONG

STRUCT tagMSG, _
 hwnd    AS ULONG, _
 message AS ULONG, _
 wParam  AS ULONG, _
 lParam  AS  LONG, _
 time    AS ULONG, _
 Pnt     AS tPnt.struct  '<--- STRUCT tPnt here


[Chris Iverson]

I don't think you can in LB.

If it's a static embed, where all the contents of the struct are embedded in the parent struct(for example, the RECT structures in the COMBOBOXINFO structure), then you can just list the individual members of the sub struct in the parent struct.

Your example would look something like this:

STRUCT tagMSG, _
 hwnd    AS ULONG, _
 message AS ULONG, _
 wParam  AS ULONG, _
 lParam  AS  LONG, _
 time    AS ULONG, _
 tPntX   AS  LONG, _
 tPntY   AS  LONG


If you need to embed a pointer to a struct, you have no choice but to embed a ULONG into the spot to get the memory address, and then use RtlMoveMemory() to copy the data from the pointer into the LB struct.

[Walt Decker]

Jul 15, 2021 13:10:46 GMT -5 Chris Iverson said:

I don't think you can in LB.

That is what I thought by the # of syntax error I received when attempting different configurations.

I hope Mr. Gundle changes that in LB5.

[Brandon Parker]

Walt,
If you really need this functionality, my Import Architect provides this type of functionality fairly easily. Feel free to check it out, and post on its forum if you like.


{:0)

Brandon Parker

[Walt Decker]

Thank you, Mr. Parker.

At the moment I do not need it, but I am sure I will need it when I get to playing around with graphics.