执行Insert语句时使用string的Format用法

SqlConnection conn = new SqlConnection("server=zzy;integrated security=sspi;database=library");
SqlCommand cmd;
private void btninsert_Click(object sender, EventArgs e)
{
conn.Open();
string _sql = "insert into login values('{0}','{1}','{2}')";

/*
Format方法：
①、string.Format(string format,object arg0);
②、string.Format(string format,params object[] args);
③、string.Format(IFormatProvider provider,string format,params object[] args);
④、string.Format(string format,object arg0,object arg1,object arg2);
*/

//④：string.Format(string format,object arg0,object arg1,object arg2);
_sql = string.Format(_sql, this.textBox1.Text.ToString().Trim(),this.textBox2.Text.ToString().Trim(),this.textBox3.Text.ToString().Trim());

/*
②：string.Format(string format,params object[] args);
object[] aa = new object[] { 'a', 'b', 'c', 'd', 'e' };
_sql = String.Format(_sql, aa);
*/
cmd = new SqlCommand(_sql, conn);
cmd.ExecuteNonQuery();
conn.Close();
MessageBox.Show("Insert the values Successfully!");
}