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How to make API/DLL calls

Since making an API call is really the same as making a DLL call, the following applies to both. In general, calling an API/DLL function works:

1) Open the desired DLL

2) Call the function or functions

3) Close the DLL

The desired DLL(s) can be opened when the program starts and closed when program execution is completed, or the DLL(s) can be opened just before calling the functions and then closed immediately afterward.

The following statements/functions are available for making API/DLL calls:

OPEN

OPEN "filename.dll" for dll as #handle

- This form of OPEN opens a desired DLL so that a program can call functions in it.

Liberty BASIC 3 has Enhanced DLL handle resolution so that if a program hasn't opened certain default Windows DLLs, a reference to a like-named handle will still resolve to the desired DLL. This will save on code to open and close DLLs. The old way still works. If a program OPENs a DLL, then it must be CLOSEd before the program ends. If the default handles below are used, then a CLOSE command should not be issued.

Here are the default handles.

#user32

#kernel32

#gdi32

#winmm

#shell32

#comdlg32

#comctl32

CALLDLL

CALLDLL #handle, "function", parm1 as type1[, parm2 as type2, ... ], result as returnType

- This statement calls a named function in an OPENed DLL The list of parameters gives information to the function that tells it how to perform its tasks.

See CallDLL.

HWND

HWND(#handle)

- This function returns a window handle for the Liberty BASIC #handle

STRUCT

STRUCT name, field1 as type1 [, field2 as type2, ... ]

The STRUCT statement builds a specified structure that is required when making some kinds of API/DLL calls. There is an example below that shows how to build a rectangle structure often used in making Windows API calls.

Constants

Liberty BASIC has a library of defined Windows constants (_SW_HIDE being one). This is equivalent to the definitions made in the windows.h file that comes with most C compilers. The way to inline a Windows constant is to take the name of the constant and place an underscore in front of it. "_SW_HIDE" is the same as the Windows constant "SW_HIDE."

If Liberty BASIC does not know the value of a Windows Constant, it will generate an undefined constant message when compiling program. In this case, the numeric value of that constant must be determined from other sources.

SAMPLE PROGRAM

Here is a short code sample (but not a complete program) using all of the above statements/functions:

NOMAINWIN

'create the structure winRect

struct winRect, _

orgX as long, _

orgY as long, _

cornerX as long, _

cornerY as long

'define sizes

openingWidth = 600

expandedHeight = 400

'open USER32.DLL

open "user32.dll" for dll as #user

button #main.showMore, "Hide Me", [hide], UL, 10, 10

open "An Example" for window as #main

#main "trapclose [quit]"

'get the window handle for #main (a standard Liberty BASIC window)

hMain = hwnd(#main)

'call the GetWindowRect API to load the window position/size into winRect

calldll #user, "GetWindowRect", _

hMain as long, _

winRect as struct, _

result as boolean

'extract the position information out of our struct

xOrg = winRect.orgX.struct

yOrg = winRect.orgY.struct

'call the MoveWindow API to resize the window to a predefined size

calldll #user, "MoveWindow", _

hMain as long, _

xOrg as long, _

yOrg as long, _

openingWidth as long, _

expandedHeight as long, _

1 as boolean, _

result as boolean

WAIT

[hide]

'get the window handle to a button in our Liberty BASIC window

hndl = hwnd(#main.showMore)

'call the ShowWindow API, passing _SW_HIDE to hide the button

calldll #user, "ShowWindow", _

hndl as long, _

_SW_HIDE as long, _

result as boolean

WAIT

[quit]

close #main

'close USER.DLL

close #user

END

In the above example, the program calls three APIs from USER32.DLL, which is a standard Windows dynamic link library.

Here's what the code does:

1) creates the structure winRect

2) opens USER32.DLL

3) gets the window handle for #main (a standard Liberty BASIC window)

4) calls the GetWindowRect API to load the window position/size into winRect

5) extracts the position information from the struct

6) calls the MoveWindow API to resize the window to a predefined size

7) gets the window handle to a button in the Liberty BASIC window

8) calls the ShowWindow API, passing _SW_HIDE to hide the button

9) closes USER32.DLL