using的几种用途

using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Generic;
using Model;
using IDAL;
using DBUnititly;

using  spacename = system.io

using system
using Introduction = system.text;
class Test
(
publ ic static int Main()
(
Introduction::NamespaceEXample NS=new Introduction::NamespaceExample()
Console.WriteLine(NS.GetNamespace());
return 0;
)

public DataSet Sedd()
{
DataSet ds = new DataSet();
using (SqlConnection sqlconntion = new SqlConnection(connectionstring))
{
sqlconntion.Open();
using (SqlCommand sqlcomm = new SqlCommand("select * from users",sqlconntion))
{
SqlDataAdapter dad = new SqlDataAdapter();
dad.SelectCommand = sqlcomm;
dad.Fill(ds);

}
}
return ds;
}