Delphi written function:
//define the function called for external StrAddStr
The function StrAddStr (inpustr: PChar; Var OutPutstr: PChar) : integer; Stdcall;
Var
Str1: string;
The begin
Str1:=inpustr;
OutPutstr:=Pchar (str1 + '+' + str1);
Showmessage (OutPutstr);
Result:=0;
end;

Vb call normal:
Public Declare Function StrAddStr Lib "Mydll. DLL" (ByVal str1 As String, ByRef str2 As String) As an Integer

Dim str1, str2 As String

Str1="A1abx"
StrAddStr str1, str2
MsgBox str2

Pb invoke exception:
The function int StrAddStr (string str1, ref string str2) library "Mydll. DLL
"
String ls_1="Axc"
String ls_2=space (20)

StrAddStr (ls_1 ls_2)
Messagebox (string (len (ls_2)), ls_2)