Question regarding exposing .net sqlbulkcopy to c++ native application

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ADO.NET

Hi, I have an application written by native c++. Now I want to use .net sqlbulkcopy function to do bulk insert without using the /clr option. I write the following .net code, and build them as intercop com.

using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Data.OleDb;
namespace comwrapper
{
    public interface Ibulkcopysql
    {
        int sqlbulkcopy(string source, string dest, string tablename);
    };
    public class bulkcopysql : Ibulkcopysql
    {
        public int sqlbulkcopy(string source, string dest, string tablename)
        {
            Console.WriteLine("enter into c# com");
            //Console.ReadKey();
            OleDbConnection sourceConnection = new OleDbConnection(source);
            String sqlselect = "SELECT * from " + tablename + ";";
            OleDbCommand commandSourceData = new OleDbCommand(sqlselect, sourceConnection);
            sourceConnection.Open();
            OleDbDataReader reader  = commandSourceData.ExecuteReader();
            SqlConnection destinationConnection = new SqlConnection(dest);
            destinationConnection.Open();
            SqlBulkCopy bulkCopy = new SqlBulkCopy(destinationConnection);
            bulkCopy.DestinationTableName = tablename;
            bulkCopy.BatchSize = 1000;
            bulkCopy.BulkCopyTimeout = 100000;
            bulkCopy.WriteToServer(reader);

            return 1;
        }
    }
}

native c++ code
#import "C:\xxxxx\bin\Debug\comwrapper.tlb" 

.......
		HRESULT hr = CoInitialize(NULL);
		cescomwrapper::IcesbulkcopysqlPtr bcpptr(__uuidof(cescomwrapper::cesbulkcopysql));
		bcpptr->sqlbulkcopy(sourcestr.AllocSysString(), deststr.AllocSysString(), tablename.AllocSysString());

......

When I try to debug the C# code, I found it enter into sqlbulkcopy function, but
break out at the following the line without giving any error message

OleDbConnection sourceConnection = new OleDbConnection(source);

Anyone know the reason?