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Use wildcard characters * and ? to compare strings

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20 Feb 2012CPOL 16.2K   6
This is much simpler: fewer new strings created, no recursion. And it allows the caller to specify how to do a string comparison.public static boolWildcardMatch( this string Subject, string Pattern, System.StringComparison...
This is much simpler: fewer new strings created, no recursion. And it allows the caller to specify how to do a string comparison.

public static bool
WildcardMatch
(
    this string             Subject
,
    string                  Pattern
,
    System.StringComparison StringComparison
)
{
    bool result = true ;

    if ( Subject == null )
    {
        throw ( new System.ArgumentNullException ( "Subject" , "Subject must not be null" ) ) ;
    }

    if ( Pattern == null )
    {
        throw ( new System.ArgumentNullException ( "Pattern" , "Pattern must not be null" ) ) ;
    }

    int soff = 0 ; /* Where we are in the Subject  */
    int poff = 0 ; /* Where we are in the Pattern  */
    int star = 0 ; /* The number of asterisks      */
    int ques = 0 ; /* The number of question marks */

    /* Traverse the Pattern */
    while ( result && ( poff < Pattern.Length ) )
    {
        switch ( Pattern [ poff ] )
        {
            /* Count any asterisks */
            case '*' :
            {
                star++ ;

                poff++ ;

                break ;
            }

            /* Count any question marks */
            case '?' :
            {
                ques++ ;

                poff++ ;

                break ;
            }

            /* Upon finding a non-wildcard */
            default :
            {
                /* Count the number of contiguous non-wildcards */
                int plen = poff ;

                while
                (
                  ( plen < Pattern.Length )
                &&
                  ( Pattern [ plen ] != '*' )
                &&
                  ( Pattern [ plen ] != '?' )
                )
                {
                    plen++ ;
                }

                plen -= poff ;

                /* Search the Subject for a matching sequence of characters */
                int slen = Subject.IndexOf
                (
                  Pattern.Substring ( poff , plen )
                ,
                  soff
                ,
                  StringComparison
                ) - soff ;

                /* The sequence must be present and must be offset by at least the number of  */
                /* question marks and may be offet by more if there was at least one asterisk */
                result = ( star == 0 ) ? ( slen == ques ) : ( slen >= ques ) ;

                /* Prepare to find more wildcards */
                soff += slen + plen ;
                poff += plen ;
                star = 0 ;
                ques = 0 ;

                break ;
            }
        }
    }

    /* Handle any trailing wildcards */
    if ( result )
    {
        int slen = Subject.Length - soff ;

        result = ( star == 0 ) ? ( slen == ques ) : ( slen >= ques ) ;
    }

    return ( result ) ;
}

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Software Developer (Senior)
United States United States
BSCS 1992 Wentworth Institute of Technology

Originally from the Boston (MA) area. Lived in SoCal for a while. Now in the Phoenix (AZ) area.

OpenVMS enthusiast, ISO 8601 evangelist, photographer, opinionated SOB, acknowledged pedant and contrarian

---------------

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Comments and Discussions

 
GeneralRe: Yeah, I use Regex quite a bit as well and wouldn't write new... Pin
PIEBALDconsult21-Feb-12 2:12
mvePIEBALDconsult21-Feb-12 2:12 
GeneralRe: I would anyways use Regex from beginning. More powerful and ... Pin
Andreas Gieriet21-Feb-12 2:08
professionalAndreas Gieriet21-Feb-12 2:08 
GeneralRe: Yes, I noticed after posting. But it looks a lot more comple... Pin
PIEBALDconsult21-Feb-12 1:58
mvePIEBALDconsult21-Feb-12 1:58 
GeneralYeah, non-greedy. string pattern = args [ 1 ].Replace ( "?"... Pin
PIEBALDconsult20-Feb-12 11:59
mvePIEBALDconsult20-Feb-12 11:59 
GeneralRe: It's a bit trickier: you have to escape the rest of the wild... Pin
Andreas Gieriet20-Feb-12 20:21
professionalAndreas Gieriet20-Feb-12 20:21 
GeneralWhile I was writing my Alternative #3 I was not sure if the ... Pin
Andreas Gieriet20-Feb-12 10:42
professionalAndreas Gieriet20-Feb-12 10:42 

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