Re: Bug in NSScanner ?

[Richard Frith-Macdonald]

On Wednesday, February 19, 2003, at 09:51  am, Manuel Guesdon wrote:

> Hi,
>
> I can't understand why this fail
>
>     NSString* str=@"( 1.3.6.1.4.1.4980.1.3.3 NAME 'oxyInetDomain' DESC 
> 'Oxymium Inet Domain' SUP oxyTop AUXILIARY MUST dc MAY ( admContact $ 
> admincontact $ billingContact $ cn $ domainCreationDate $ labeledURL $ 
> mailRelayedBy $ managerEMail $ nic $ nichandle $ registrant $ soa $ 
> techContact $ domaindescription $ oxymiumReferenceDisplay $ 
> associatedServices $ associatedrootentity $ associatedmanagemententity 
> $ associatedrootcompany $ associatedmanagemententityrights $ 
> associatedrootentityrights $ associatedrootcompanyrights $ parkmessage 
> $ logoURL ) )";
>       NSScanner *aScanner = [NSScanner scannerWithString:str];
>
>       if (0)     // If 1, it works !
>         {
>           BOOL upTo1=[aScanner scanUpToString:@"MUST "
>                                intoString:NULL];
>           NSLog(@"upTo1=%d",upTo1);
>           if (upTo1)
>             {
>               BOOL scan1=[aScanner scanString:@"MUST "
>                                    intoString:NULL];
>               NSLog(@"scan1=%d",scan1);
>               if (scan1)
>                 {
>                   NSString* must=nil;
>                   [aScanner scanUpToString:@" "
>                             intoString:&must];
>                 }
>             };
>         };
>       NSLog(@"scanLocation=%u",[aScanner scanLocation]);
>       NSLog(@"scan=[%@]",[[aScanner string] 
> substringFromIndex:[aScanner scanLocation]]);
>       BOOL upTo2=[aScanner scanUpToString:@"MAY "
>                           intoString:NULL];
>       NSLog(@"upTo2=%d",upTo2);
>       if (upTo2)
>         {
>           BOOL scan2=[aScanner scanString:@"MAY "
>                           intoString:NULL];
>           NSLog(@"scan2=%d",scan2);
>         };
>
>
> I try to scan str for differents components. If I scan directly up to 
> MAY, it works. If I scan for must and next scan
> for may, it doesn't works.
> May be my code is wrong but I can't see why :-)

After you scan the word 'MUST', you then tell the scanner to scan up to 
a space .... but a space is in the set of characters to be skipped, and 
the MacOS-X documentation of -charactersToBeSkipped says that behavior 
in this case is undefined.  In fact the GNUstep behavior is 
well-defined ... characters from this set are always skipped before 
scanning starts, even if you are scanning for something thsst is in the 
set.
The scan location is at a space (which is skipped) then everything up 
to the next space is scanned, leaving the scan location at the space 
immediately before 'MAY'

Next you say to scan up to 'MAY' ... so the space at the scan location 
is skipped, then the scanner encounters 'MAY', so no characters are 
scanned and the method returns NO.

You use this return status to decide whether to scan in 'MAY', and 
because it is NO you don't scan it in.

So ... it's all working as documented ... and I believe this is also 
how MacOS-X works.