RUBY TIMES FOR THE ERROR HANDLING STRUCTURE

       It is very happy to come back . This time , we will learn about RUBY  ERROR  HANDLING  STRUCTURE.If you were a C/C++  programmer,it  is very simple. ERROR  HANDLING  STRUCTURE is the same between  C/C++  and RUBY.It is sure that  the key word is different.OK, let's start our RUBY time.

      

      BEGIN

         ..........

         ..........

          RESCUE

               RAISE

               RETRY

          ELSE

          ENSURE

      END

     We should face that  no matter how carefully we wrote our programs ,some unforeseen errors will still  be encourtered .But don't worry

about that.Every programming language  exists ERROR handling  struture. As ruby ,the main frame of error handling  is above.

    If you want to catch the exception generated in  your new code , first of all, to tell effect area is very important.Ruby traps exceptions when it find the keyword "begin",and will finish this job with "end ".There are many types of exception.Different exceptions deals with different methods.So how to tell  ruby that ? We can use "rescue"  to let exception match dealing method.Most of time.there will not be only one exception existing.As a result ,  what exception we predict ,what method is on call.

    The more exception happen in program , the more rescue should be match in exception handling.when you want to read the H disk,but your pc does not exist H disk.At this time , runtime gives out an ErrNO "ENOENT".On my pc , D: is  my DVD  driver. There is no disk in it ,when my program tries to log on to DVD driver,Ruby returns this type of ERROR "EACCES".There are a variety of Errno, you rescue them in different case.In fact,you can rescue all type of Errnos in your program.Some of them will be effect ,so it must to find out which is need.or else you will waste your times to write uneffect code.

    RAISE is easy to understand . Do you  still remember "catch"  in C++? yes, they are the same.Exceptions will be thrown by runtime when logic is out of control.At this time , Ruby checks every rescue to compare with them .Matching successfully,Ruby excutes RAISE method  and runtime stop to wait method finish.

   The main effect of RETRY is to let rumtime back to the first of the program . Ruby points to the start and excutes again.Why it needs to redo .I don't know.

   Sometimes , an error happens , runtime catches  it , then check out whether there is method to deal with it in the RESCUE.There is a lot of errers   during  the proceduce runing of  program . It does not exist  a structure to handling all of the error. Consequently,ELSE is nessary when an unknow error generated. It could be a method or a tips of the error.

   ENSURE which is like its name's meaning can confirm the following  code will be excute. You can print error message in RESCUE.All error handling logic set in ENSURE.