Re: cin.fail() , ignore() , clear()...

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 10 Feb 2011 17:05:46 CST

Message-ID:

<8f342617-bc61-43a0-98c0-c7f42d47bd02@k22g2000yqh.googlegroups.com>

On Feb 9, 11:24 pm, TheGunslinger <mikiesrunsbaal....@sbcglobal.net>
wrote:

[...]

I finally went with the following code snippet:

  //-------------------------------------
        do{
            try{
        cout<<"How many days to be rented?\n";
        cin>>daysRented;
        if(cin.fail()){
            throw false;
        }else{goodInput=true;}
        }catch(bool IOerror){
        goodInput=false;
        cin.clear();
        cin.ignore(20,'\n');
            } //End try/throw/catch
        }while(goodInput==false);
//--------------------------------------

which was most effective in catching bad user input errors.

I'm not sure what you mean by "most effective" (and I can easily
enter text for which it would fail), but it certainly looks like
serious abuse of exceptions. If I could afford to ignore end of
file and possible hard errors, I'd use something like:

   int
   getInt( std::istream& source )
   {
       int result;
       source >> result;
       while ( !source ) {
           source.clear();
           source.ignore(INT_MAX, '\n');
           source >> result;
       }
       return result;
   }

A more realistic version would be:

   Fallible<int>
   getInt( char const* promptInCaseOfError, std::istream& source )
   {
       Fallible<int> result;
       bool fatalErrorSeen = false;
       while ( !fatalErrorSeen && !result.isValid() ) {
           int tmp;
           source >> tmp;
           if ( source ) {
               result.validate( tmp );
           } else if ( source.bad() || source.eof() ) {
               fatalErrorSeen = true;
           } else {
               source.clear();
               source.ignore( INT_MAX, '\n' );
               if ( promptInCaseOfError != NULL ) {
                   std::cout << prompt;
                   std::cout.flush();
               }
           }
       }
       return result;
   }

--
James Kanze

--
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]