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hsearch (3)
  • hsearch (3) ( Solaris man: Библиотечные вызовы )
  • >> hsearch (3) ( FreeBSD man: Библиотечные вызовы )
  • hsearch (3) ( Русские man: Библиотечные вызовы )
  • hsearch (3) ( Linux man: Библиотечные вызовы )
  • hsearch (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    hcreate , hdestroy , hsearch
    
     - manage hash search table
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <search.h>
    int hcreate (size_t nel);
    void hdestroy (void);
    ENTRY * hsearch (ENTRY item ACTION action);
     

    DESCRIPTION

    The hcreate (,);
    hdestroy (,);
    and hsearch ();
    functions manage hash search tables.

    The hcreate ();
    function allocates sufficient space for the table, and the application should ensure it is called before hsearch ();
    is used. The Fa nel argument is an estimate of the maximum number of entries that the table should contain. This number may be adjusted upward by the algorithm in order to obtain certain mathematically favorable circumstances.

    The hdestroy ();
    function disposes of the search table, and may be followed by another call to hcreate (.);
    After the call to hdestroy (,);
    the data can no longer be considered accessible. The hdestroy ();
    function calls free(3) for each comparison key in the search table but not the data item associated with the key.

    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 Fa item argument is a structure of type Vt ENTRY (defined in the    #include <search.h>
    header) containing two pointers: Fa item.key points to the comparison key (a Vt char * ) , and Fa item.data (a Vt void * ) points to any other data to be associated with that key. The comparison function used by hsearch ();
    is strcmp(3). The Fa action argument is a member of an enumeration type Vt ACTION indicating the disposition of the entry if it cannot be found in the table. ENTER indicates that the Fa 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.

    The comparison key (passed to hsearch ();
    as Fa item.key ) must be allocated using malloc(3) if Fa action is ENTER and hdestroy ();
    is called.  

    RETURN VALUES

    The hcreate ();
    function returns 0 if the table creation failed and the global variable errno is set to indicate the error; otherwise, a non-zero value is returned.

    The hdestroy ();
    function does not return a value.

    The hsearch ();
    function returns a NULL pointer if either the Fa action is FIND and the Fa item could not be found or the Fa action is ENTER and the table is full.  

    EXAMPLES

    The following example reads in strings followed by two numbers and stores them in a hash table, discarding duplicates. It then reads in strings and finds the matching entry in the hash table and prints it out.
    #include <stdio.h>
    #include <search.h>
    #include <string.h>
    #include <stdlib.h>
    
    struct info {                   /* This is the info stored in the table */
            int age, room;          /* other than the key. */
    };
    
    #define NUM_EMPL        5000    /* # of elements in search table. */
    
    int
    main(void)
    {
            char str[BUFSIZ]; /* Space to read string */
            struct info info_space[NUM_EMPL]; /* Space to store employee info. */
            struct info *info_ptr = info_space; /* Next space in info_space. */
            ENTRY item;
            ENTRY *found_item; /* Name to look for in table. */
            char name_to_find[30];
            int i = 0;
    
            /* Create table; no error checking is performed. */
            (void) hcreate(NUM_EMPL);
    
            while (scanf("%s%d%d", str, &info_ptr->age,
                &info_ptr->room) != EOF && i++ < NUM_EMPL) {
                    /* Put information in structure, and structure in item. */
                    item.key = strdup(str);
                    item.data = info_ptr;
                    info_ptr++;
                    /* Put item into table. */
                    (void) hsearch(item, ENTER);
            }
    
            /* Access table. */
            item.key = name_to_find;
            while (scanf("%s", item.key) != EOF) {
                    if ((found_item = hsearch(item, FIND)) != NULL) {
                            /* If item is in the table. */
                            (void)printf("found %s, age = %d, room = %d\n",
                                found_item->key,
                                ((struct info *)found_item->data)->age,
                                ((struct info *)found_item->data)->room);
                    } else
                            (void)printf("no such employee %s\n", name_to_find);
            }
            hdestroy();
            return 0;
    }
    
     

    ERRORS

    The hcreate ();
    and hsearch ();
    functions may fail if:

    Bq Er ENOMEM
    Insufficient storage space is available.
    Bq Er EINVAL
    A table already exists.

     

    SEE ALSO

    bsearch(3), lsearch(3), malloc(3), strcmp(3), tsearch(3)  

    STANDARDS

    The hcreate (,);
    hdestroy (,);
    and hsearch ();
    functions conform to St -xpg4.2 .  

    HISTORY

    The hcreate (,);
    hdestroy (,);
    and hsearch ();
    functions first appeared in AT&T System V .  

    BUGS

    The interface permits the use of only one hash table at a time.


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    EXAMPLES
    ERRORS
    SEE ALSO
    STANDARDS
    HISTORY
    BUGS


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