How to return List from c# method and Use the List return values in c++ can u give guidance how to do it??
I going like following way my complete scenario:
in c# DemoLib.cs
usng System;using System.Collections.Generic;
public interface IDiscover
{
void GetList1();
String GetList2();
List<string> GetList3();
};
namespace DemoLibrary
{
class DemoLib
{
public void GetList1()
{
Console.WriteLine(" I am from Void GetList()");
}
public string GetList2()
{
Console.WriteLine(" I am from string GetList()");
return "Stack OverFlow";
}
public List<string> GetList3()
{
List<string> li=new List<string>();
li.Add("India");
li.Add("America");
li.Add("London");
Console.WriteLine(" I am from List<string> GetList()");
return li;
}
Build successfully and created DemoLib.dll
I copy the DemoLib.dll to c:\DemoLib.dll and using regasm created Demolib.tlb in c:\
Now in Vc++ i Hav main()
DemoLibMain.vc++
#include<list>
#include<stdio.h>
void main()
{
HRESULT Hr=CoInitialize(NULL);
IDiscoverPtr Iptr(__uuidof(DemoLib));
Iptr->GetList1();
std::string str=Iptr->GetList2();
printf("%s",str); //dispalys "null" insted of "stack overflow" but when i debugging it
shows the value "stack overflow" at str.
Iptr->(Afraid since it doesnot give GetList3() )
when i forced to write Iptr->GetList3() it Display the error as
GetList3 is not a member of IDiscover;
I did it using the object type of c#
C# exported as COM
public void GetList(ref object list)
{
String[] dummy = { "1" };
Array.Resize(ref dummy, 3);
list = dummy;
}
Native C++
_variant_t list;
GetList(list);
const VARTYPE type (static_cast<VARTYPE>(list.vt & VT_TYPEMASK));
const bool isArray (0 != (list.vt & VT_ARRAY));
const bool isVector(0 != (list.vt & VT_VECTOR));
if(isArray) {
SAFEARRAY* buffer = src.parray;
...
}
Problem here is that a SAFEARRAY isn't accessible by vbscript. But its no problem for most other languages.
Same question yesterday:
How to return a collection of strings from C# to C++ via COM interop
(Short answer: List won't be included in the COM interface because it uses a generic type).
When you import a tlb in VC++ and compile it, an intermediate file is generated with extension .tlh in your intermediate directory (normally debug/release directory depending upon your current configuration) . This is sort of a proxy file and contains all the methods that you can call. Have a look at this file and this will give you the exact syntax of what should be passed.
As far as your method GetList2 is concerned, it is returning a simple string which translates to a BSTR in the generated tlb so you need to get the return value in a BSTR. For GetList3 since you are returning an array, therefore, most probably the return type in .tlh file will be a variant containing an array of BSTRs. The vt of the variant will most probably be VT_ARRAY|VT_BSTR. You can loop-through this array in the variant and get all the values one-by-one.
EDIT: As somebody else suggested that it is List<>, therefore, it won't get translated to a COM Type. IMO, your best option is to use ArrayList instead of using List<>
Another Edit: I just checked and ArrayList does not get translated to any of the COM Automation types. In this case your best bet is to use a simple string array, cast it to object and return that object from your method. This object will be converted to a variant containing a SafeArray of BSTRs. You will need to loop-through that safearray to get your data.
