---
name: "hcreate"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/hcreate"
---

# hcreate(3)

manage hash search table

## NAME

**hcreate**, **hdestroy**, **hsearch** – manage hash search table

## LIBRARY

Standard C Library (libc, -lc)

## 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 *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)](/free/3.md) 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 *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(3)](/strcmp/3.md). 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. Unsuccessful resolution is indicated by the return of a NULL pointer.

The comparison key (passed to **hsearch**() as *item.key*) must be allocated using [malloc(3)](/malloc/3.md) if *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 *action* is FIND and the *item* could not be found or the *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:

- \[ENOMEM\]

  Insufficient storage space is available.

- \[EINVAL\]

  A table already exists.

## SEE ALSO

[bsearch(3)](/bsearch/3.md), [lsearch(3)](/lsearch/3.md), [malloc(3)](/malloc/3.md), [strcmp(3)](/strcmp/3.md), [tsearch(3)](/tsearch/3.md)

## STANDARDS

The **hcreate**(), **hdestroy**(), and **hsearch**() functions conform to X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”).

## HISTORY

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

## BUGS

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