AT&T UNIX™PC Unix System V Users Manual - tenox

HSEARCH ( 3C ) HSEARCH ( 3C )
NAME
hsearch, hcreate, hdestroy - manage hash search tables
SYNOPSIS
#include
ENTRY •hsearch (item, action)
ENTRY item;
ACTION action;
int hcreate (nel)
unsigned nel;
void hdestroy ( )
DESCRIPTION
Hs earch is a hash-table search routine generalized from Knuth
(6.4) Algorithm D. It returns a pointer into a hash table indicating
the location at which an entry can be found. Item is a structure
of type ENTRY (defined in the header file) containing
two pointers: item.key points to the comparison key, and
item. data points to any other data to be associated with that key.
(Pointers to types other than character should be cast to pointerto-character.)
Action is a member of an enumeration type
ACTION indicating the disposition of the entry if it cannot be
found in the table. ENTER indicates that the item should be
inserted in the table at an appropriate point. FIND indicates that
no entry should be made. Unsuccessful resolution is indicated by
the return of a NULL pointer.
Hcreate allocates sufficient space for the table, and must be called
before hsearch is used. Nel is an estimate of the maximum
number of entries that the table will contain. This number may
be adjusted upward by the algorithm in order to obtain certain
mathematically favorable circumstances.
Hdestroy destroys the search table, and may be followed by
another call to hcreate .
NOTES
Hsearch uses open addressing with a multiplicative hash function.
However, its source code has many other options available which
the user may select by compiling the hsearch source with the following
symbols defined to the preprocessor:
DIV Use the remainder modulo table size as the
hash function instead of the multiplicative
algorithm.
USCR Use a User Supplied Comparison Routine for
ascertaining table membership. The routine
should be named hcompar and should
behave in a manner similar to strcmp (see
string(3C)).
CHAINED Use a linked list to resolve collisions. If this
option is selected, the following other options
become available.
- 1-