In geometry sheet it should looks like for each element if it works.
the api is
FHoudiniApi::SetAttributeFloatArrayData(
NodeId,
ParentId,
TCHAR_TO_ANSI(*AttribName),
&AttribInfo,
Array.GetData(),
Array.Num(),
SizeFixedArray.GetData(),
0,
SizesFixedArray.Num());

for example I have two points, and I want to create an empty float array attribute for them. I just set AttribInfo.count to 2, tuple size to 1. totalArrayElements to 0. SizeFixedArray to {0,0}. Array is Empty. Is it rigth? Or should I set SizeFixedArray empty? Or just create the attribute but do not set? Or it is not valid to create an empty array attrib?