How do I create a variant array of BSTR in Euphoria using EuCOM?

Question

So far I've figured out how to pass Unicode strings, bSTRs, to and from a Euphoria DLL using a Typelib. What I can't figure out, thus far, is how to create and pass back an array of BSTRs.

The code I have thus far (along with includes for EuCOM itself and parts of Win32lib):

global function REALARR()
  sequence seq
  atom psa
  atom var
  seq = { "cat","cow","wolverine" }
  psa = create_safearray( seq, VT_BSTR )
  make_variant( var, VT_ARRAY + VT_BSTR, psa )
  return var
end function

Part of the typelib is:

  [
     helpstring("get an array of strings"), 
     entry("REALARR")
  ] 
  void __stdcall REALARR( [out,retval] VARIANT* res );

And the test code, in VB6 is:

...
Dim v() as String
V = REALARR()
...

So far all I've managed to get is an error '0' from the DLL. Any ideas? Anyone?

Answer 1

I've been in touch with the Euphoria people via their forum, and have gotten this far. The routine is failing on the the make_variant line. I haven't figured it out any further than that and neither have they.

global function REALARR() 
  atom psa 
  atom var 
  atom bounds_ptr 
  atom dim 
  atom bstr 
  object void 

  dim = 1 
  bounds_ptr = allocate( 8 * dim ) -- now figure out which part is Extent and which is LBound 
  poke4( bounds_ptr, { 3, 0 } ) -- assuming Extent and LBound in that order 

  psa = c_func( SafeArrayCreate, { VT_BSTR, 1, bounds_ptr } ) 

  bstr = alloc_bstr( "cat" ) 
  poke4( bounds_ptr, 0 ) 
  void = c_func( SafeArrayPutElement, {psa, bounds_ptr, bstr}) 
  free_bstr( bstr ) 

  bstr = alloc_bstr( "cow" ) 
  poke4( bounds_ptr, 1 ) 
  void = c_func( SafeArrayPutElement, {psa, bounds_ptr, bstr}) 
  free_bstr( bstr ) 

  bstr = alloc_bstr( "wolverine" ) 
  poke4( bounds_ptr, 2 ) 
  void = c_func( SafeArrayPutElement, {psa, bounds_ptr, bstr}) 
  free_bstr( bstr ) 

  make_variant( var, VT_ARRAY + VT_BSTR, psa )  
  return var 
end function

Answer 2

Okay, var hasn't been initialised. Not that it matters as the routine still crashes. Nevertheless, one needs a

var = allocate( 16 )

just before the make_variant

Answer 3

You should use the create_safearray() function. It's documented (hidden?) under Utilities. Basically, put your BSTR pointers into a sequence and pass it to create_safearray():

sequence s, bstrs
s = {"A", "B"}
bstrs = {}
for i = 1 to length(s) do
    bstrs &= alloc_bstr( s[i] )
end for

atom array
array = create_safearray( bstrs, VT_BSTR )

...

destroy_safearray( array )