An FTN95 DLL that is called by an executable that uses the STDCALL calling convention (e.g. one created using Win32 Visual Basic) must use F_STDCALL in the declaration of all exported subprograms. For example,
F_STDCALL FUNCTION F(X)
INTEGER F,X
F=X
END
Such a function could make calls to Windows API functions provided an interface is provided via, for example, 'USE MSWIN' or 'INCLUDE <windows.ins>'. Alternatively an interface for each API function can be given explicitly. For example,
STDCALL SENDMESSAGE 'SendMessageA' (VAL,VAL,VAL,VAL):INTEGER*4
A call is automatically made to a DLL function called LIBMAIN when the DLL is loaded. If you do not provide a definition of LIBMAIN then SLINK will provide a default for you. LIBMAIN is used to initialise global data. It takes the following form.
F_STDCALL INTEGER FUNCTION LIBMAIN(hInst,ul,lpR)
INTEGER hInst,ul,lpR
!***** Initialise global data here
LIBMAIN=1
END
A simple SLINK script would take the form:
dll
lo f95.obj
exportall
file c:\windows\f95.dll
A Visual Basic program can use calls to the API functions LoadLibrary and FreeLibrary in order to ensure that the DLL does not unload whilst a Visual Basic form is loaded. Here is some sample code for this purpose.
Private Declare Function LoadLibrary Lib 'kernel32' Alias 'LoadLibraryA' (ByVal s As String) As Long
Private Declare Function FreeLibrary Lib 'kernel32' (h As Long) As Long
Dim hLibModule As Long
Private Sub Form_Load()
hLibModule = LoadLibrary('f95.dll')
End Sub
Private Sub Form_Unload(Cancel As Integer)
i& = FreeLibrary(hLibModule)
End Sub
-- Admin Silverfrost Limited