March 30, 2005
Here is trap for young players ...

int find(dchar[] ToScan, dchar[] ToFind)
{
  for( int lPos = 0; lPos <= (ToScan.length - ToFind.length); lPos++)
    {
        if (ToScan[lPos .. lPos + ToFind.length] == ToFind)
            return lPos;
    }
    return -1;
}


See the bug? Neither did I until I tested it with ...

  assert( find("xxx", "abcdef") == -1);

The problem is that the expression ("xxx".length - "abcdef".length) is *not* a negative number. And thus it failed to exit the 'for' loop cleanly; instead it crashed with an ArrayBoundsError!

So now I've got ...

int find(dchar[] ToScan, dchar[] ToFind)
{
    if (ToScan.length == 0)
        return -1;

    if (ToFind.length == 0)
        return -1;

    if (ToFind.length > ToScan.length)
        return -1;

    for( int lPos = 0; lPos <= (ToScan.length - ToFind.length); lPos++)
    {
        if (ToScan[lPos .. lPos + ToFind.length] == ToFind)
            return lPos;
    }
    return -1;
}

Oh well, live and learn.

-- 
Derek Parnell
Melbourne, Australia
http://www.dsource.org/projects/build/
http://www.prowiki.org/wiki4d/wiki.cgi?FrontPage
30/03/2005 10:34:52 AM
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