I have a third-party (Win32) DLL, written in C, that exposes the following interface:
DLL_EXPORT typedef enum
{
DEVICE_PCI = 1,
DEVICE_USB = 2
} DeviceType;
DLL_EXPORT int DeviceStatus(DeviceType kind);
I wish to call it from Delphi.
How do I get access to the DeviceType constants in my Delphi code? Or, if I should just use the values 1 and 2 directly, what Delphi type should I use for the "DeviceType kind" parameters? Integer? Word?
The usual way to declare the interface from an external DLL in C is to expose its interface in a .H header file. Then, to access the DLL from C the .H header file has to be #included in the C source code.
Translated to Delphi terms, you need to create a unit file that describes the same interface in pascal terms, translating the c syntax to pascal.
For your case, you would create a file such as...
unit xyzDevice;
{ XYZ device Delphi interface unit
translated from xyz.h by xxxxx -- Copyright (c) 2009 xxxxx
Delphi API to libXYZ - The Free XYZ device library --- Copyright (C) 2006 yyyyy }
interface
type
TXyzDeviceType = integer;
const
xyzDll = 'xyz.dll';
XYZ_DEVICE_PCI = 1;
XYZ_DEVICE_USB = 2;
function XyzDeviceStatus ( kind : TXyzDeviceType ) : integer; stdcall;
external xyzDLL; name 'DeviceStatus';
implementation
end.
And the you would declare it in the uses clause of your source code. And invoke the function this way:
uses xyzDevice;
...
case XyzDeviceStatus(XYZ_DEVICE_USB) of ...
Default underlying type for enum in C++ is int (unsigned 32 bits). You need to define the same parameter type in Delphi. Regarding enumerated values, you can use hard-coded 1 and 2 values to call this function from Delphi, or use any other Delphi language feature (enum? constant? I don't know this language) which gives the same result.
Sure, you can use Integer and pass constanst directly, but it is more safe to declare function with using usual enum type. It should be like this (note "MINENUMSIZE" directive):
{$MINENUMSIZE 4}
type
TDeviceKind = (DEVICE_PCI = 1, DEVICE_USB = 2);
function DeviceStatus(kind: TDeviceKind): Integer; stdcall; // cdecl?
DEVICE_PCI will equal 0, not 1. You need to insert a dummy like DEVICE_UNKNOWN for value 0, or give the value 1 to the first enum.
