How to pass a nil in place of a const record?

Question

I am trying to call the WIC (Windows Imaging Component) factory method `CreateEncoder`: ``` HRESULT CreateEncoder( [in] REFGUID guidContainerFormat, [in, optional] const GUID *pguidVendor, [out, retval] IWICBitmapEncoder **ppIEncoder ); ``` The general idea would be: ``` var encoder: IWICBitmapEncoder; CreateEncoder( GUID_ContainerFormatIco, //The GUID for the desired container format nil, //No preferred codec vendor {out}encoder); ``` For the second parameter, i want to pass `nil`; to indicate that i have no encoder preference But Delphi's translation of the WinCodec.pas is: ``` function CreateEncoder(const guidContainerFormat: TGuid; const pguidVendor: TGUID; out ppIEncoder: IWICBitmapEncoder): HRESULT; stdcall; ``` You'll notice that the second parameter, the optional `TGUID`, is declared as `const`. So how do i pass it nil? How can i pass a `nil` where a `const` record is required? I tried the naïve solution: ``` const NULL_GUID: TGUID = (); factory.CreateEncoder(GUID_ContainerFor…

Accepted Answer

You can use something like this:

```
const
  NULL_PGUID: PGUID = nil;
begin
  factory.CreateEncoder(GUID_ContainerFormatIco, NULL_PGUID^, {out}encoder);
end;
```

Or as Sertac suggested, the shorter and sweeter version:

```
factory.CreateEncoder(GUID_ContainerFormatIco, PGUID(nil)^, {out}encoder);
```

I did a test and David's suggestion of:

```
factory.CreateEncoder(GUID_ContainerFormatIco, TGUID(nil^), {out}encoder);    
```

Also works.

How to pass a nil in place of a const record?

Solution

Problem