---
name: "hsearch"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/hcreate"
---

# hsearch(3)

manage hash search table

Part of [hcreate(3)](/hcreate/3.md).

## NAME

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

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<search.h\>**

*int*\

**hcreate**(*size\_t nel*);

*int*\

**hcreate\_r**(*size\_t nel*, *struct hsearch\_data \*table*);

*void*\

**hdestroy**(*void*);

*void*\

**hdestroy\_r**(*struct hsearch\_data \*table*);

*ENTRY* *\**\

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

*int*\

**hsearch\_r**(*ENTRY item*, *ACTION action*, *ENTRY \*\* itemp*, *struct hsearch\_data \*table*);

## DESCRIPTION

The **hcreate**(), **hcreate\_r**(), **hdestroy**(), **hdestroy\_r**() **hsearch**(), and **hsearch\_r**() 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. As this implementation resizes the hash table dynamically, this argument is ignored.

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 disposes of the search table but does not free the comparison keys or data items stored in it. The caller is responsible for freeing any memory associated with table entries before calling **hdestroy**().

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) that contains 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.

The **hcreate\_r**(), **hdestroy\_r**(), and **hsearch\_r**() functions are re-entrant versions of the above functions that can operate on a table supplied by the user. The **hsearch\_r**() function returns 0 if the action is ENTER and the element cannot be created, 1 otherwise. If the element exists or can be created, it will be placed in *itemp*, otherwise *itemp* will be set to NULL.

## RETURN VALUES

The **hcreate**() and **hcreate\_r**() functions return 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**() and **hdestroy\_r**() functions return no value.

The **hsearch**() and **hsearch\_r**() functions return 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**(), **hcreate\_r**(), **hsearch**(), and **hsearch\_r**() functions will fail if:

- \[ENOMEM\]

  Insufficient memory is available.

The **hsearch**() and **hsearch\_r**() functions will also fail if the action is FIND and the element is not found:

- \[ESRCH\]

  The *item* given is not found.

## 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. The **hcreate\_r**(), **hdestroy\_r**() and **hsearch\_r**() functions are GNU extensions.

## BUGS

The original, non-GNU interface permits the use of only one hash table at a time.