HIDAPI.pas

Free Pascal bindings for libhidapi on Linux

only Linux (or other *ixes)

This does not (yet) work on Windows, it assumes sizeof(wchar_t) == 4 and this is not true on Windows. Also the library name will be different and I did not have a Windows PC with hidapi.dll at hand when writing this, on Windows I usually just use CreateFile(), ReadFile(), WriteFile() functions and the SetupAPI to enumerate the devices.

Usage

I have chosen the more Pascal-like SomeObject.FooBar(baz) style of porting this API instead of the naked and rather ugly C-ish some_object_foo_bar(some_object, baz) notation for this API. This results in much nicer code when using it. It also allows to convert some unwieldy things like wchar_t* to more convenient UnicodeString on the fly.

The HIDAPI (like most object oriented C-APIs) will use pointers to structs as handles for objects and all API calls (methods of the struct) will expect this pointer as first argument. This is the typical C-style of object oriented programming. Free Pascal allows us to define these structs as Pascal objects and these can have our own methods attached to them (with more Pascalish naming conventions and more Pascalish parameter types) which will then in turn be implemented as wrappers to the original C api functions.

For best experience you should set the modeswitch

{$modeswitch autoderef}

Use the API like this:

var
  Paths: TSringList;
  LinkedList, Item: PHidDeviceInfo;
  
begin
  Paths := TStringList.Create();
  LinkedList := THidDeviceInfo.Enumerate($DEAD, $BEEF);
  Item := LinkedList;
  while Assigned(Item) do begin
    Paths.Append(Item.Path);
    Item := Item.Next;
  end;
  LinkedList.Free;
  
  
  // now you have a list of paths
  
end;

Or when opening a device from a Path you could do it like this:

var
  Device: PHidDevice;
  Buffer: array[0..63] of Byte;
  
begin
  Device := THidDevice.OpenPath(SomePath);
  if Assigned(Device) then begin
    if Device.Read(Buffer, SizeOf(Buffer)) > 0 then begin
      WriteLn('Success, got some Data');
    end;
    
    // do more stuff with the device
    
    Device.Close;
  end;
end;

Without the autoderef modeswitch you would have to write it like Device^.Read or LinkedList^.Free, this looks ugly, the autoderef will dereference the pointer to the object automatically.