dtSearch Text Retrieval Engine Programmer's Reference
dtsFileSpec::excludeFilters Data Member
const char * excludeFilters;

Filename filters used to exclude files in selected directories. Must point to a null-delimited string set, terminated by a double-null. If not used, initialize to 0. 

Filename filters containing a slash (/ or \) are matched against the full path and filename. Filename filters without a slash (/ or \) are matched against only the filename.