eCos Reference Manual
`Chapter 38. TCP/IP Library Reference
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`gethostbyname
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`GETHOSTBYNAME(3) System Library Functions Manual GETHOSTBYNAME(3)
`NAME
` gethostbyname, gethostbyname2, gethostbyaddr, gethostent, sethostent,
` endhostent, hstrerror, herror - get network host entry
`SYNOPSIS
` #include <netdb.h>
` extern int h_errno;
` struct hostent *
` gethostbyname(const char *name);
` struct hostent *
` gethostbyname2(const char *name, int af);
` struct hostent *
` gethostbyaddr(const char *addr, int len, int af);
` struct hostent *
` gethostent(void);
` void
` sethostent(int stayopen);
` void
` endhostent(void);
` void
` herror(const char *string);
` const char *
` hstrerror(int err);
`DESCRIPTION
` The gethostbyname() and 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 information obtained from the name server (i.e., resolver(3) and
` named(8)), broken-out fields from a line in /etc/hosts, or database
` entries supplied by the yp(8) system. resolv.conf(5) describes how the
` particular database is chosen.
` 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 */
` };
`
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` #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.
` 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 com-
` patibility.
` The function gethostbyname() will search for the named host in the cur-
` rent domain and its parents using the search lookup semantics detailed in
` resolv.conf(5) and hostname(7).
` gethostbyname2() is an advanced form of gethostbyname() which allows
` lookups in address families other than AF_INET, for example AF_INET6.
` The gethostbyaddr() function will search for the specified address of
` length len in the address family af. The only address family currently
` supported is AF_INET.
` The sethostent() function 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(). Other-
` wise, queries are performed using UDP datagrams.
` The endhostent() function closes the TCP connection.
` The herror() function prints an error message describing the failure. If
` its argument string is non-null, it is prepended to the message string
` and separated from it by a colon (`:') and a space. The error message is
` printed with a trailing newline. The contents of the error message is
` the same as that returned by hstrerror() with argument h_errno.
`FILES
` /etc/hosts
` /etc/resolv.conf
`DIAGNOSTICS
` Error return status from gethostbyname(), gethostbyname2(), 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 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 authori-
`
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` tative 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.
`SEE ALSO
` resolver(3), getaddrinfo(3), getnameinfo(3), hosts(5), resolv.conf(5),
` hostname(7), named(8)
`CAVEAT
` If the search routines in resolv.conf(5) decide to read the /etc/hosts
` file, gethostent() and other functions will read the next line of the
` file, re-opening the file if necessary.
` The sethostent() function opens and/or rewinds the file /etc/hosts. If
` the stayopen argument is non-zero, the file will not be closed after each
` call to gethostbyname(), gethostbyname2(), or gethostbyaddr().
` The endhostent() function closes the file.
`HISTORY
` The herror() function appeared in 4.3BSD. The endhostent(),
` gethostbyaddr(), gethostbyname(), gethostent(), and sethostent() func-
` tions appeared in 4.2BSD.
`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 formats are currently understood.
` YP does not support any address families other than AF_INET and uses the
` traditional database format.
`BSD March 13, 1997 BSD
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