| Standards / Extensions | C or C++ | Dependencies |
|---|---|---|
XPG4 |
both |
#define _XOPEN_SOURCE
#include <search.h>
ENTRY *hsearch(ENTRY item, ACTION action);The hsearch() function is a hash-table search routine. It returns a pointer into a hash table indicating the location at which an entry can be found. The item argument is a structure of type ENTRY (defined in the <search.h> header) containing two pointers: item.key points to the comparison key (a char * ), and item.data (a void * ) points to any other data to be associated with that key. The comparison function used by hsearch() is strcmp(). The action argument 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.
Threading Behavior: The hcreate() function allocates a piece of storage for use as the hash table. This storage is not exposed to the user, and is referred to by all threads. In other words, these functions operate on one hash table global to the process. The library serializes access to the table and attendant data across threads using an internal mutex.
hsearch() returns a NULL pointer if either the action is FIND and the item could not be found or the action is ENTER and the table is full.