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GETHOSTBYNAME
!!!GETHOSTBYNAME
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
FILES
CONFORMING TO
NOTES
SEE ALSO
----
!!NAME


gethostbyname, gethostbyaddr, sethostent, endhostent, herror, hstrerror - get network host entry
!!SYNOPSIS


__#include
__''name''__);
struct hostent *gethostbyname2(const char *__''name''__, int__ ''af''__);
#include
__''addr''__,
int__ ''len''__, int__ ''type''__);
void sethostent(int__ ''stayopen''__);
void endhostent(void);
void herror(const char *__''s''__);
const char * hstrerror(int__ ''err''__);
__
!!DESCRIPTION


The __gethostbyname()__ function returns a structure of
type ''hostent'' for the given host ''name''. Here
''name'' is either a host name, or an IPv4 address in
standard dot notation, or an IPv6 address in colon (and
possibly dot) notation. (See RFC 1884 for the description of
IPv6 addresses.) If ''name'' is an IPv4 or IPv6 address,
no lookup is performed and __gethostbyname__() simply
copies ''name'' into the ''h_name'' field and its
''struct in_addr'' equivalent into the
''h_addr_list[[0]'' field of the returned ''hostent''
structure. If ''name'' doesn't end in a dot and the
environment variable __HOSTALIASES__ is set, the alias
file pointed to by __HOSTALIASES__ will first be searched
for ''name'' (see hostname(7) for the file
format). The current domain and its parents are searched
unless ''name'' ends in a dot.


The __gethostbyaddr()__ function returns a structure of
type ''hostent'' for the given host address ''addr''
of length ''len'' and address type ''type''. The only
valid address type is currently __AF_INET__.


The __sethostent()__ function specifies, if
''stayopen'' is true (1), that a connected TCP socket
should be used for the name server queries and that the
connection should remain open during successive queries.
Otherwise, name server queries will use UDP
datagrams.


The __endhostent()__ function ends the use of a TCP
connection for name server queries.


The (obsolete) __herror()__ function prints the error
message associated with the current value of ''h_errno''
on stderr.


The (obsolete) __hstrerror()__ function takes an error
number (typically ''h_errno'') and returns the
corresponding message string.


The domain name queries carried out by
__gethostbyname()__ and __gethostbyaddr()__ use a
combination of any or all of the name server
named(8), a broken out line from ''/etc/hosts'',
and the Network Information Service (NIS or YP), depending
upon the contents of the ''order'' line in
''/etc/host.conf''. (See __resolv+__(8)). The default
action is to query named(8), followed by
''/etc/hosts''.


The ''hostent'' structure is defined in
'''' as follows:


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 */
}
#define h_addr  h_addr_list[[0]  /* for backward compatibility */


The members of the ''hostent'' structure
are:


''h_name''


The official name of the host.


''h_aliases''


A zero-terminated array of alternative names for the
host.


''h_addrtype''


The type of address; always __AF_INET__ at
present.


''h_length''


The length of the address in bytes.


''h_addr_list''


A zero-terminated array of network addresses for the host in
network byte order.


''h_addr''


The first address in ''h_addr_list'' for backward
compatibility.
!!RETURN VALUE


The __gethostbyname()__ and __gethostbyaddr()__
functions return the ''hostent'' structure or a NULL
pointer if an error occurs. On error, the ''h_errno''
variable holds an error number.
!!ERRORS


The variable ''h_errno'' can have the following
values:


__HOST_NOT_FOUND__


The specified host is unknown.


__NO_ADDRESS__ or __NO_DATA__


The requested name is valid but does not have an IP
address.


__NO_RECOVERY__


A non-recoverable name server error occurred.


__TRY_AGAIN__


A temporary error occurred on an authoritative name server.
Try again later.
!!FILES


''/etc/host.conf''


resolver configuration file


''/etc/hosts''


host database file
!!CONFORMING TO


BSD 4.3.
!!NOTES


The functions __gethostbyname__() and
__gethostbyaddr__() may return pointers to static data,
which may be overwritten by later calls. Copying the
''struct hostent'' does not suffice, since it contains
pointers - a deep copy is required.


The SUS-v2 standard is buggy and declares the ''len''
parameter to be of type ''size_t''. (That is wrong,
because it has to be ''int'', and ''size_t'' is not.
The Austin draft makes it ''socklen_t'', which is
OK.)


Glibc2 also has a


__struct hostent *gethostbyname2(const char *__''name''__, int__ ''af''__);
__that works like __gethostbyname()__, but permits to specify the address family to which the address must belong.


The Austin draft marks __gethostbyaddr()__ and
__gethostbyname()__ legacy, and introduces


__struct hostent *getipnodebyaddr (const void *restrict__ ''addr''__,
socklen_t__ ''len''__, int__ ''type''__, int *restrict__ ''error_num''__);
struct hostent *getipnodebyname (const char *__''name''__,
int__ ''type''__, int__ ''flags''__, int *__''error_num''__);
__
!!SEE ALSO


resolver(3), hosts(5), hostname(7),
__resolv+__(8), named(8)
----
5 pages link to gethostbyaddr(3):
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Version 1, saved on Tuesday, June 4, 2002 12:24:22 am by "perry"
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