gethostbyname(SLIB) 6 January 1993 gethostbyname(SLIB) Name endhostent, gethostbyname, gethostbyaddr, herror - get network host entry Syntax #include <netdb.h> extern int h_errno; struct hostent *gethostbyname(name) char *name; struct hostent *gethostbyaddr(addr, len, type) char *addr; int len, type; sethostent(stayopen) int stayopen; endhostent() herror(string) char *string; Description gethostbyname and gethostbyaddr each returns 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(ADMN), or broken-out fields from a line in /etc/hosts. If the local name server is not running these rou- tines 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: hname Official name of the host. haliases A null-terminated array of alternate names for the host. haddrtype The type of address being returned; currently always AF_INET. hlength The length, in bytes, of the address. haddrlist A null-terminated array of network addresses for the host. Host addresses are returned in network byte order. haddr The first address in haddrlist; this is for backward com- patibility. 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(ADMN) for the domain search procedure and the alias file format. 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 gethost- byname or gethostbyaddr. Otherwise, queries are performed using UDP datagrams. endhostent closes the TCP connection. Diagnostics Error return status from gethostbyname and gethostbyaddr is indicated by return of a null pointer. The external integer herrno 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. herrno can have the following values: HOSTNOTFOUND No such host is known. TRYAGAIN 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. NORECOVERY Some unexpected server failure was encountered. This is a non-recoverable error. NODATA 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. Files /etc/hosts Notes 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 under- stood. See also hosts(SFF), hostname(ADMN), named(ADMN), and resolver(SLIB).