GETHOSTBYNAME

Section: C Library Functions (3)
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BSD mandoc
BSD 4.2

NAME

gethostbyname gethostbyaddr gethostent sethostent endhostent herror - get network host entry

SYNOPSIS

Fd #include <netdb.h> Fd extern int h_errno; Ft struct hostent * Fn gethostbyname const char *name Ft struct hostent * Fn gethostbyaddr const char *addr int len int type Ft struct hostent * Fn gethostent void Fn sethostent int stayopen Fn endhostent void Fn herror char *string

DESCRIPTION

The Fn gethostbyname and Fn gethostbyaddr functions each return a pointer to an object with the following structure describing an internet host referenced by name or by address, respectively. This structure contains either the information obtained from the name server, named(8), broken-out fields from a line in /etc/hosts or database entries supplied by the yp(8) system . 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:

Fa h_name

Official name of the host.

Fa h_aliases

A zero terminated array of alternate names for the host.

Fa h_addrtype

The type of address being returned; currently always AF_INET

Fa h_length

The length, in bytes, of the address.

Fa h_addr_list

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

Fa h_addr

The first address in Fa h_addr_list ; this is for backward compatibility.

When using the nameserver, Fn gethostbyname will search for the named host in the current domain and its parents unless the name ends in 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) for the domain search procedure and the alias file format.

The Fn sethostent function may be used to request the use of a connected TCP socket for queries. If the Fa 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 Fn gethostbyname or Fn gethostbyaddr . Otherwise, queries are performed using UDP datagrams.

The Fn endhostent function closes the TCP connection.

FILES

/etc/hosts

DIAGNOSTICS

Error return status from Fn gethostbyname and Fn 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 Fn herror can be used to print an error message describing the failure. If its argument Fa string is non -NULL it is printed, followed by a colon and a space. The error message is printed with a trailing newline.

The variable h_errno can have the following values:

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.
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.

CAVEAT

The Fn gethostent function is defined, and Fn sethostent and Fn endhostent are redefined, when libc(3) is built to use only the routines to lookup in /etc/hosts and not the name server.

The Fn gethostent function reads the next line of /etc/hosts opening the file if necessary.

The Fn sethostent function opens and/or rewinds the file /etc/hosts If the Fa stayopen argument is non-zero, the file will not be closed after each call to Fn gethostbyname or Fn gethostbyaddr .

The Fn endhostent function closes the file.

HISTORY

The Fn herror function appeared in BSD 4.3 The Fn endhostent , Fn gethostbyaddr , Fn gethostbyname , Fn gethostent , and Fn sethostent functions appeared in BSD 4.2

BUGS

These functions use static data storage; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Only the Internet address format is currently understood.

This document was created by man2html, using the manual pages.
Time: 19:42:00 GMT, December 25, 2022