"extern int h_errno;

"struct hostent *gethostbyname(name)

"char *name;

"struct hostent *gethostbyname2(name, af)

"char *name; int af;

"struct hostent *gethostbyaddr(addr, len, type)

"char *addr; int len, type;

"struct hostent *gethostent()

"sethostent(stayopen)

"int stayopen;

"endhostent()

"herror(string)

"char *string;

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:

\w'h_addr_list'u+2n h_name Official name of the host.

\w'h_addr_list'u+2n h_aliases A zero terminated array of alternate names for the host.

\w'h_addr_list'u+2n h_addrtype The type of address being returned; usually AF_INET.

\w'h_addr_list'u+2n h_length The length, in bytes, of the address.

\w'h_addr_list'u+2n h_addr_list A zero terminated array of network addresses for the host. Host addresses are returned in network byte order.

\w'h_addr_list'u+2n 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 the current domain and its parents unless the name ends in a dot. If the name contains no dot, and if the environment variable ``HOSTALAIASES'' 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.

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 \s-2NULL\s+2 after having set h_errno to \s-2NETDB_INTERNAL\s+2.

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.

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:

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.