Delphi 2010: EOleSysError 'Type mismatch' calling ActiveX control

Question

I have this C ActiveX API (don't have the sources just the binaries):

// \param a [out] Variant holding a byte array 
// \param b [out] Reference to a longlong (Signed 64-bit)
// \param c [out] Reference to a short
short foo(variant* a, longlong* b, short* c);

It's working fine in C#:

//auto-generated import:   
short foo(ref object a, ref long b, ref short c);

test {
 object a=null;
 long b=0;
 short c=0;
 foo(a,b,c); => OK 
}

NOK in Delphi 2010 (Note that {??Int64}OleVariant is added by the Delphi import tool):

//auto-generated import:
function foo(var a: OleVariant; 
             var b: {??Int64}OleVariant; 
             var c: Smallint): Smallint;

procedure Test;
var
 a, b: OleVariant;
 c: Smallint;
begin
 foo(a,b,c); => **EOleSysError 'Type mismatch' exception**
end;

Answer 1

You can use predefined WinAPI types:

// C definition
short foo(variant* a, longlong* b, short* c);

// Delphi definition
function foo(var a: OleVariant; 
             var b: LongLong; 
             var c: Smallint); Smallint;

procedure FooTest;
var
  a: OleVariant;
  b: LongLong;
  c, RetVal: ShmallInt;
begin
  Retval := foo(a, b, c);
end;

LongLong is defined in Windows.pas, along with many, many other WinAPI compatible types. (At least they're in the Windows unit up through Delphi XE; XE2 may have relocated some of them due to cross-platform and 64-bit related relocations.)

// Windows.pas definition (Delphi 2010)
type
  LONGLONG = int64;

As David keeps mentioning in the comments below, longlong isn't a standard C++ datatype. However, based on the comments related to the parameters in your update, it's exactly what the C++ developer intended it to be, and therefore the WinAPI definition is compatible (and retains the same name for consistency for documentation purposes).