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Use wildcard characters * and ? to compare strings

, 20 Feb 2012 CPOL
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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)

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About the Author

PIEBALDconsult
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
 
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Comments and Discussions

 
GeneralRe: Yeah, I use Regex quite a bit as well and wouldn't write new... PinmemberPIEBALDconsult21-Feb-12 3:12 
GeneralRe: I would anyways use Regex from beginning. More powerful and ... PinmemberAndreas Gieriet21-Feb-12 3:08 
I would anyways use Regex from beginning. More powerful and less chance for mistake. Performance is far less an issue that many people "fear" - I never had to replace regex by some hand-crafted solution since it was too slow.
 
I wonder if anyone really did do measurments to compare the solutions...
GeneralRe: Yes, I noticed after posting. But it looks a lot more comple... PinmemberPIEBALDconsult21-Feb-12 2:58 
GeneralYeah, non-greedy. string pattern = args [ 1 ].Replace ( "?"... PinmemberPIEBALDconsult20-Feb-12 12:59 
GeneralRe: It's a bit trickier: you have to escape the rest of the wild... PinmemberAndreas Gieriet20-Feb-12 21:21 
GeneralWhile I was writing my Alternative #3 I was not sure if the ... PinmemberAndreas Gieriet20-Feb-12 11:42 

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