NAME

       af_initset,  af_nrofkeys,  af_setgkey,  af_setaddkey, af_setrmkey, af_setposrmkey, af_sortset, af_subset,
       af_copyset, af_intersect, af_union, af_diff - AtFS operations on key sets

SYNOPSIS

       #include <atfs.h>

       int af_initset (Af_set *set)

       int af_nrofkeys (Af_set *set)

       int af_setgkey (Af_set *set, int position, Af_key *key)

       int af_setaddkey (Af_set *set, int position, Af_key *key)

       int af_setrmkey (Af_set *set, Af_key *key)

       int af_setposrmkey (Af_set *set, int position)

       int af_sortset (Af_set *set, char *attrname)

       int af_subset (Af_set *set, Af_attrs *attrbuf, Af_set *subset)

       int af_copyset (Af_set *source, Af_set *destination)

       int af_intersect (Af_set *set1, Af_set *set2, Af_set *newset)

       int af_union (Af_set *set1, Af_set *set2, Af_set *newset)

       int af_diff (Af_set *set1, Af_set *set2, *Af_set newset)

DESCRIPTION

       Sets in AtFS are ordered collections of keys. The structure of sets is the following

              typedef struct {
                   int  af_nkeys;
                   int  af_setlen;
                   Af_key    *af_klist;
              } Af_set;

       The list of keys in a set is a linear list, residing in allocated memory. The list has no holes, so  that
       positions  0  through  af_nkeys-1  are  occupied with valid keys. Set functions returning a set require a
       pointer to an empty set structure as argument.

       af_initset initializes a set.

       af_nrofkeys returns the number of valid keys in the given set.

       af_setgkey delivers the filekey, stored at position position in the identified set. The result is  passed
       in the buffer key. Typically you use af_setgkey to run through a set and perform a special action on each
       key.  The following code sequence does this job:
            Af_key key;
            Af_set set;
            af_initset (&set);
            ...
            for (i = 0; i < af_nrofkeys (&set); i++) {
                 af_setgkey (&set, i, &key);
                 /* process key */
                 ...
            }

       af_setaddkey introduces a new filekey to an existing set at the given position. All  following  keys  are
       moved  back  by one position.  The constant AF_LASTPOS given as position argument leads to adding the new
       filekey at the end of the set.

       af_setrmkey (af_setposrmkey) removes the given filekey  (the  filekey  at  position  position)  from  the
       specified  set.  Holes generated by deleting single keys from a set are eliminated by condensing the set.
       All following keys are moved one position forth in the set.

       af_sortset sorts a given set of object keys by the values of the named attribute. The set  is  sorted  in
       increasing  order.   Increasing  order  means,  that  the  lowest value occurs first in the set.  Af_user
       structures are compared by username first and by userdomain, if the names are equal (user host  will  not
       be taken into account).  Version numbers are ordered in natural order, busy versions first.

       In  atfs.h  you  can  find  a list of attribute names naming the standard attributes. All other attribute
       names are presumed to be user defined attributes.  While  sorting  by  the  values  of  an  user  defined
       attribute,  all  ASOs that do not have the named attribute are added at the end of the resulting (sorted)
       set.  Sorting of user defined attributes with multiple values bases on simple text  comparison  with  the
       order  of  the  values  taken as it is.  The length of the given attribute name is limited. This limit is
       defined by the constant AF_UDANAMLEN in atfs.h.

       af_subset does a retrieve operation (similar to af_find - manual page af_retrieve(3)) on a given  set  of
       object  keys.  Af_subset  takes  an  attribute  buffer  (attrbuf)  with  all desired attributes set to an
       appropriate value as argument. The attribute buffer should be initialized by  af_initattrs  (manual  page
       af_retrieve(3))  beforehand.  af_subset  returns  it's  result  in  a  new  set, the original set remains
       unchanged.

       af_copyset for copying sets (really! =:-).

       af_intersect, af_union and af_diff build intersections, unions, and differences between  two  sets.   The
       result  is  a  new set, where all keys taken from the first argument set (set1) occur first, and the keys
       from the second argument set (set2) afterwards. You may gibe one of set1 or set2 as  resultset.  In  that
       case, the original set get lost and is dropped implicitely.

       Sets  generated  by  af_copyset,  af_subset,  af_intersect,  af_union,  or  af_diff should be released by
       af_dropset as soon as they are not used any longer.

SEE ALSO

       af_retrieve(3)

DIAGNOSTICS

       Upon error, -1 or a nil pointer (depending on the return type) is returned and af_errno  is  set  to  the
       corresponding error number.