Interfacing with DLLs
Using EiffelStudio, there are two different ways to call C routines exported in DLLs. This is because on the Windows platform, there are two frequently-used calling conventions for C routines found in DLLs:
- _cdecl: referred to as the standard calling convention
- __stdcall referred to as the Pascal calling convention
Calling conventions define 1) how arguments are placed on the stack, and 2) which entity (the caller, or the callee) is responsible for returning the call stack to its previous state when the routine has completed. These two methods are NOT compatible. Therefore if you have a routine in a DLL you wish to call, one of the first things to find out about it is which calling convention it expects. DLL routines that use the
_cdecl calling convention require the use of the dll32 sub-language option. For
__stdcall, use the dllwin32 sub-language option. Here is an example:
my_cdecl_routine (a: INTEGER): POINTER
-- Encapsulation of a dll function with the `_cdecl' call mechanism.
"C [dll32 %"my_cdecl_dll.dll%"] (int): EIF_POINTER"
my_stdcall_routine (a: INTEGER): POINTER
-- Encapsulation of a dll function with the `_stdcall' call mechanism.
"C [dllwin32 %"my_stdcall_dll.dll%"] (int): EIF_POINTER"