C#数据库连接字符串放到配置文件出现问题
C#数据库连接字符串放到配置文件app.config后在conn.open处出问题，new SqlConnection(str)中的str改回"server=.\\SQL2005; database=clxdb;  integrated security=True"就没有问题，MessageBox.Show(str);显示server=.\\SQL2005; database=clxdb;  integrated security=True，求大神指点
app.config文件内容

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

  <connectionStrings>

    <add name="abc" connectionString="server=.\\SQL2005; database=clxdb;  integrated security=True"/>

  </connectionStrings>

</configuration>

Button1按钮

        private void button1_Click(object sender, EventArgs e)

        {

            string str = ConfigurationManager.ConnectionStrings["abc"].ConnectionString;

            //

            using (SqlConnection conn = new SqlConnection(str))

            {MessageBox.Show(str);

                if(conn!=null && conn.State!=ConnectionState.Open)

                conn.Open();

                using (SqlCommand cmd = conn.CreateCommand())

                {

                    cmd.CommandText = "select * from manager";

                    using(SqlDataReader reader=cmd.ExecuteReader())

                    while (reader.Read())

                    {

                        string strreader=reader.GetString(0);

                        MessageBox.Show(strreader);

                    }