GETHOSTBYNAME(3) UNIX Programmer's Manual GETHOSTBYNAME(3) NAME gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent, herror - get network host entry SYNOPSIS #include extern int h_errno; struct hostent *gethostbyname(name) char *name; struct hostent *gethostbyaddr(addr, len, type) char *addr; int len, type; struct hostent *gethostent() sethostent(stayopen) int stayopen; endhostent() herror(string) char *string; DESCRIPTION _G_e_t_h_o_s_t_b_y_n_a_m_e and _g_e_t_h_o_s_t_b_y_a_d_d_r 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, _n_a_m_e_d(8), or broken-out fields from a line in /_e_t_c/_h_o_s_t_s. If the local name server is not running these routines do a lookup in /_e_t_c/_h_o_s_t_s. 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; currently always AF_INET. Printed 11/26/99 October 30, 1996 1 GETHOSTBYNAME(3) UNIX Programmer's Manual GETHOSTBYNAME(3) 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 compatiblity. When using the nameserver, _g_e_t_h_o_s_t_b_y_n_a_m_e 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 _h_o_s_t_n_a_m_e(7) for the domain search procedure and the alias file format. _S_e_t_h_o_s_t_e_n_t may be used to request the use of a connected TCP socket for queries. If the _s_t_a_y_o_p_e_n 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 _g_e_t_h_o_s_t_- _b_y_n_a_m_e or _g_e_t_h_o_s_t_b_y_a_d_d_r. Otherwise, queries are performed using UDP datagrams. _E_n_d_h_o_s_t_e_n_t closes the TCP connection. DIAGNOSTICS Error return status from _g_e_t_h_o_s_t_b_y_n_a_m_e and _g_e_t_h_o_s_t_b_y_a_d_d_r is indicated by return of a null pointer. The external integer _h__e_r_r_n_o may then be checked to see whether this is a tem- porary failure or an invalid or unknown host. The routine _h_e_r_r_o_r can be used to print an error message describing the failure. If its argument _s_t_r_i_n_g is non-NULL, it is printed, followed by a colon and a space. The error message is printed with a trailing newline. _h__e_r_r_n_o 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 authorita- tive 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 Printed 11/26/99 October 30, 1996 2 GETHOSTBYNAME(3) UNIX Programmer's Manual GETHOSTBYNAME(3) 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. FILES /etc/hosts SEE ALSO resolver(3), hosts(5), hostname(7), named(8) CAVEAT _G_e_t_h_o_s_t_e_n_t is defined, and _s_e_t_h_o_s_t_e_n_t and _e_n_d_h_o_s_t_e_n_t are redefined, when _l_i_b_c is built to use only the routines to lookup in /_e_t_c/_h_o_s_t_s and not the name server. _G_e_t_h_o_s_t_e_n_t reads the next line of /_e_t_c/_h_o_s_t_s, opening the file if necessary. _S_e_t_h_o_s_t_e_n_t is redefined to open and rewind the file. If the _s_t_a_y_o_p_e_n argument is non-zero, the hosts data base will not be closed after each call to _g_e_t_h_o_s_t_b_y_n_a_m_e or _g_e_t_h_o_s_t_b_y_a_d_d_r. _E_n_d_h_o_s_t_e_n_t 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 for- mat is currently understood. Printed 11/26/99 October 30, 1996 3