---
name: "gethostbyname"
section: "3bind"
platform: "linux"
package: "bind-dev"
version: "1:8.4.7-1"
release: "Debian 4.0 (Etch)"
platforms: ["linux"]
url: "https://new.carta.tech/gethostbyname/3bind"
---

# gethostbyname(3bind)

get network host entry

## NAME

**gethostbyname**, **gethostbyaddr**, **gethostent**, **sethostent**, **endhostent**, **herror** – get network host entry

## SYNOPSIS

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

*extern* *int*\
 *h\_errno*;

*struct* *hostent* *\**\

**gethostbyname**(*char \*name*);

*struct* *hostent* *\**\

**gethostbyname2**(*char \*name*, *int af*);

*struct* *hostent* *\**\

**gethostbyaddr**(*char \*addr*, *int len, type*);

*struct* *hostent* *\**\

**gethostent**();

**sethostent**(*int stayopen*);

**endhostent**();

**herror**(*char \*string*);

## DESCRIPTION

**Gethostbyname**(), **gethostbyname2**(), and **gethostbyaddr**() each return a pointer to a *hostent* structure (see below) describing an internet host referenced by name or by address, as the function names indicate. This structure contains either the information obtained from the name server, [named(8)](/named/8.md), or broken-out fields from a line in  */etc/hosts*. If the local name server is not running, these routines do a lookup in */etc/hosts*.

```
struct	hostent {
	char	*h_name;	/* official name of host */
	char	**h_aliases;	/* alias list */
	int	h_addrtype;	/* host address type */
	int	h_length;	/* length of address */
	char	**h_addr_list;	/* list of addresses from name server */
};
#define	h_addr  h_addr_list[0]	/* address, for backward compatibility */
```

The members of this structure are:

- h\_name

  Official name of the host.

- h\_aliases

  A zero-terminated array of alternate names for the host.

- h\_addrtype

  The type of address being returned; usually  AF\_INET.

- h\_length

  The length, in bytes, of the address.

- h\_addr\_list

  A zero-terminated array of network addresses for the host. Host addresses are returned in network byte order.

- h\_addr

  The first address in  h\_addr\_list; this is for backward compatibility.

When using the nameserver, **gethostbyname**() will search for the named host in each parent domain given in the  “search” directive of [resolv.conf(5)](/resolv.conf/5.md) unless the name contains a dot (“.”). If the name contains no dot, and if the environment variable  HOSTALIASES contains the name of an alias file, the alias file will first be searched for an alias matching the input name. See [hostname(7)](/hostname/7.md) for the domain search procedure and the alias file format.

**Gethostbyname2**() is an evolution of **gethostbyname**() intended to allow lookups in address families other than  AF\_INET, for example,  AF\_INET6. Currently, the *af* argument must be specified as AF\_INET else the function will return  NULL after having set *h\_errno* to  NETDB\_INTERNAL.

**Sethostent**() may be used to request the use of a connected TCP socket for queries. If the *stayopen* flag is non-zero, this sets the option to send all queries to the name server using TCP and to retain the connection after each call to  **gethostbyname**() or **gethostbyaddr**(). Otherwise, queries are performed using UDP datagrams.

**Endhostent**() closes the TCP connection.

## ENVIRONMENT

- HOSTALIASES

  Name of file containing  (*host* *alias*, *full* *hostname*) pairs.

## FILES

- */etc/hosts*

  See [hosts(5)](/hosts/5.md).

## DIAGNOSTICS

Error return status from  **gethostbyname**() and **gethostbyaddr**() is indicated by return of a null pointer. The external integer *h\_errno* may then be checked to see whether this is a temporary failure or an invalid or unknown host. The routine **herror**() can be used to print an error message describing the failure. If its argument *string* is non-NULL, it is printed, followed by a colon and a space. The error message is printed with a trailing newline.

*h\_errno* can have the following values:

- NETDB\_INTERNAL

  This indicates an internal error in the library, unrelated to the network or name service. *errno* will be valid in this case; see perror(2).

- HOST\_NOT\_FOUND

  No such host is known.

- TRY\_AGAIN

  This is usually a temporary error and means that the local server did not receive a response from an authoritative server. A retry at some later time may succeed.

- NO\_RECOVERY

  Some unexpected server failure was encountered. This is a non-recoverable error, as one might expect.

- NO\_DATA

  The requested name is valid but does not have an IP address;  this is not a temporary error.   This means that the name is known to the name server but there is no address associated with this name. Another type of request to the name server using this domain name will result in an answer; for example, a mail-forwarder may be registered for this domain.

## SEE ALSO

[hosts(5)](/hosts/5.md), [hostname(7)](/hostname/7.md), [named(8)](/named/8.md), [resolver(3)](/resolver/3.md), [resolver(5)](/resolver/5.md).

## CAVEAT

**Gethostent**() is defined, and **sethostent**() and **endhostent**() are redefined, when *libc* is built to use only the routines to lookup in */etc/hosts* and not the name server:

**Gethostent**() reads the next line of */etc/hosts*, opening the file if necessary.

**Sethostent**() is redefined to open and rewind the file.  If the *stayopen* argument is non-zero, the hosts data base will not be closed after each call to **gethostbyname**() or **gethostbyaddr**().

**Endhostent**() is redefined to close the file.

## BUGS

All information is contained in a static area so it must be copied if it is to be saved.  Only the Internet address format is currently understood.