"int cfunc(void) " how can I call this function with "ruby/dl'

Ruby
1

In ruby/dl (win32)

I define the function like the belows.

require ‘dl’
libc=DL.open(“libfunc.dll”)
func=libc[‘func_test’,‘IO’] # int func_test(void);

Then, I typed in irb like the belows.

func.call()

But the error message is displayed

‘1 arguments are need’

So, I type in irb like this

func.call(nil)

But, the error message is also displayed.

‘DL::DLTypeError: unknown type ‘0’ of the return value.’

I’m not sure how to call this function in ruby/dl

Please let me know the reason and solutions.

Thank you in advance.