the max length of a column?

hello,in my database I have a column with the type varchar(500),
but when I used as followings to get the length of the column , I get 255 ?
     pcol->name=dbcolname(m_pdbprocess,j);
     pcol->type=dbcoltype(m_pdbprocess,j);
     pcol->size=dbcollen(m_pdbprocess,j);   -----this is just 255? while I
has a 500 length column.

I tried more length column such as varchar(1000), but dbcollen only turns
255 to me,why?
And how can I fixed the bug? Thanks~