CONTENTS

SYNOPSIS

"int hcreate(size_t "nel);

"ENTRY *hsearch(ENTRY "item", ACTION "action);

"void hdestroy(void);"

#define _GNU_SOURCE
#include <search.h>

"int hcreate_r(size_t "nel", struct hsearch_data *"tab);

"int *hsearch_r(ENTRY "item", ACTION "action, "ENTRY **"ret", struct hsearch_data *"tab);

First the table must be created with the function hcreate(). The argument nel is an estimate of the maximum number of entries in the table. The function hcreate() may adjust this value upward to improve the performance of the resulting hash table.

The corresponding function hdestroy() frees the memory occupied by the hash table so that a new table can be constructed.

The argument item is of type ENTRY, which is a typedef defined in <search.h> and includes these elements:

typedef struct entry {
char *key;
void *data;
} ENTRY;

hsearch() returns NULL if action is ENTER and the hash table is full, or action is FIND and item cannot be found in the hash table.

"CONFORMS TO"

BUGS

The following program inserts 24 items in to a hash table, then prints some of them.

#include <stdio.h>
#include <search.h>

char *data[] = { "alpha", "bravo", "charlie", "delta",
"echo", "foxtrot", "golf", "hotel", "india", "juliet",
"kilo", "lima", "mike", "november", "oscar", "papa",
"quebec", "romeo", "sierra", "tango", "uniform",
"victor", "whisky", "x-ray", "yankee", "zulu"
};

int main() {
ENTRY e, *ep;
int i;

/* starting with small table, and letting it grow does not work */
hcreate(30);
for (i = 0; i < 24; i++) {
e.key = data[i];
/* data is just an integer, instead of a
pointer to something */
e.data = (char *)i;
ep = hsearch(e, ENTER);
/* there should be no failures */
if (ep == NULL) {
fprintf(stderr, "entry failed\n");
exit(1);
}
}
for (i = 22; i < 26; i++) {
/* print two entries from the table, and
show that two are not in the table */
e.key = data[i];
ep = hsearch(e, FIND);
printf("%9.9s -> %9.9s:%d\n", e.key,
ep ? ep->key : "NULL",
ep ? (int)(ep->data) : 0);
}
return 0;
}