作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

                （1）结构化异常处理:：
                           try
                            ...........
                            catch
                            ............
                            flnally
                            ................
                            end try
                  其中Catch的结构有三种：Catch、Catch...As 和 Catch...When。其中Catch...As 和 Catch...When 子句捕捉特定的异常，并允许相关的语句块指定应用程序如何处理。
                     例：（登录界面部分代码）
                      Dim sqlconn as New sqlcliet.sqlconnection(configurationsettings.appsettings("connectionstring"))
                     Dim select_string as string="select * from user where user_name='" & trim(user_name.text) & "' and user_pwd='" & trim(user_pwd.text) & "' " 
                      Dim select_comm as New sqlclient.sqlcommand(select_string,sqlconn)
                      Dim select_reader as sqlclient.sqldatareader

                      try
                        sqlconn.open()
                        select_reader=selec_comm.executereader(commandbehaviorcloseconnection)
                        if select_reader.read()=true then
                              dim username as string
                              session("username")=trim(user_name.text)
                              response.redirect("mian.aspx")
                              select_reader.close()
                              sqlconn.close()
                        else
                              response.write("<script langusge='javascript' runat='server'>window.alert('用户名或密码错误错误!')</script>")
                        end if
                       catch sqlexc as execption
                            response.write("错误发生!"&sqlexc.tostring())
                       finally
                            if not select_reader is nothing then
                                    select_reader.close()
                            end if
                  (2)非结构化异常处理：通过Error对象及On Error、Resume和Error三种语句实现。
                     例：
                      On Error Resume Next
           Err.Clear
           Err.Raise（33333）
           Err.Description = "您没有输入数字！"
                      MsgBox（Err.Number）
                      MsgBox（Err.Description）
                        

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