Cross post here

Since function LibraryFunctionLoad can load a function from .dll file like

fun = LibraryFunctionLoad["demo", "demo_I_I", {Integer}, Integer]

Then you can use fun in Mathematica. And I can know this function demo_I_I from this .dll LibraryFunctionInformation[fun]

{"ReturnType" -> Integer, "ArgumentTypes" -> {Integer},"File" -> 
  "C:\\Program Files\\Wolfram \
Research\\Mathematica\\11.1zh\\SystemFiles\\Links\\LibraryLink\\\
LibraryResources\\Windows-x86-64\\demo.dll", "Function" -> "demo_I_I"}

But how to know how many function can be loaded in this demo.dll file.And how to know its form of parameter?