NAME
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NAME
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gethostbyname, gethostbyaddr, herror, hstrerror - get network host entry
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gethostbyname, gethostbyaddr, herror, hstrerror - get network host entry
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SYNOPSIS
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SYNOPSIS
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#include <network.h>
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#include <network.h>
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struct hostent *gethostbyname(const char *name);
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struct hostent *gethostbyname(const char *name);
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struct hostent *gethostbyaddr(const char *addr, int len, int type);
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struct hostent *gethostbyaddr(const char *addr, int len, int type);
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void herror(const char *s);
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void herror(const char *s);
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const char * hstrerror(int err);
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const char * hstrerror(int err);
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DESCRIPTION
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DESCRIPTION
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The gethostbyname() function returns a structure of type
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The gethostbyname() function returns a structure of type
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hostent for the given host name. Here name is either a
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hostent for the given host name. Here name is either a
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host name, or an IPv4 address in standard dot notation, or
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host name, or an IPv4 address in standard dot notation, or
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an IPv6 address in colon (and possibly dot) notation. (See
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an IPv6 address in colon (and possibly dot) notation. (See
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RFC 1884 for the description of IPv6 addresses.) If name
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RFC 1884 for the description of IPv6 addresses.) If name
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is an IPv4 or IPv6 address, no lookup is performed and
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is an IPv4 or IPv6 address, no lookup is performed and
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gethostbyname() simply copies name into the h_name field
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gethostbyname() simply copies name into the h_name field
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and its struct in_addr equivalent into the h_addr_list[0]
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and its struct in_addr equivalent into the h_addr_list[0]
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field of the returned hostent structure. If name doesn't
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field of the returned hostent structure. If name doesn't
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end in a dot and the environment variable HOSTALIASES is
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end in a dot and the environment variable HOSTALIASES is
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set, the alias file pointed to by HOSTALIASES will first
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set, the alias file pointed to by HOSTALIASES will first
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be searched for name. (See hostname(7) for the file for
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be searched for name. (See hostname(7) for the file for
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mat.) The current domain and its parents are searched
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mat.) The current domain and its parents are searched
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unless name ends in a dot.
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unless name ends in a dot.
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The gethostbyaddr() function returns a structure of type
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The gethostbyaddr() function returns a structure of type
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hostent for the given host address addr of length len and
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hostent for the given host address addr of length len and
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address type type. The only valid address type is cur
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address type type. The only valid address type is cur
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rently AF_INET.
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rently AF_INET.
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The (obsolete) herror() function prints the error message
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The (obsolete) herror() function prints the error message
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associated with the current value of h_errno on stderr.
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associated with the current value of h_errno on stderr.
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The (obsolete) hstrerror() function takes an error number
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The (obsolete) hstrerror() function takes an error number
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(typically h_errno) and returns the corresponding message
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(typically h_errno) and returns the corresponding message
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string.
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string.
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The domain name queries carried out by gethostbyname() and
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The domain name queries carried out by gethostbyname() and
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gethostbyaddr() use a combination of any or all of the
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gethostbyaddr() use a combination of any or all of the
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name server named(8), a broken out line from /etc/hosts,
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name server named(8), a broken out line from /etc/hosts,
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and the Network Information Service (NIS or YP), depending
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and the Network Information Service (NIS or YP), depending
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upon the contents of the order line in /etc/host.conf.
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upon the contents of the order line in /etc/host.conf.
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(See resolv+(8)). The default action is to query
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(See resolv+(8)). The default action is to query
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named(8), followed by /etc/hosts.
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named(8), followed by /etc/hosts.
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The hostent structure is defined in <netdb.h> as follows:
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The hostent structure is defined in <netdb.h> as follows:
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struct hostent {
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struct hostent {
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char *h_name; /* official name of host */
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char *h_name; /* official name of host */
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char **h_aliases; /* alias list */
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char **h_aliases; /* alias list */
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int h_addrtype; /* host address type */
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int h_addrtype; /* host address type */
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int h_length; /* length of address */
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int h_length; /* length of address */
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char **h_addr_list; /* list of addresses */
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char **h_addr_list; /* list of addresses */
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}
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}
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#define h_addr h_addr_list[0] /* for backward compatibility */
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#define h_addr h_addr_list[0] /* for backward compatibility */
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The members of the hostent structure are:
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The members of the hostent structure are:
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h_name The official name of the host.
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h_name The official name of the host.
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h_aliases
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h_aliases
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A zero-terminated array of alternative names for
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A zero-terminated array of alternative names for
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the host.
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the host.
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h_addrtype
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h_addrtype
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The type of address; always AF_INET at present.
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The type of address; always AF_INET at present.
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h_length
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h_length
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The length of the address in bytes.
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The length of the address in bytes.
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h_addr_list
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h_addr_list
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A zero-terminated array of network addresses for
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A zero-terminated array of network addresses for
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the host in network byte order.
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the host in network byte order.
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h_addr The first address in h_addr_list for backward com
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h_addr The first address in h_addr_list for backward com
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patibility.
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patibility.
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RETURN VALUE
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RETURN VALUE
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The gethostbyname() and gethostbyaddr() functions return
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The gethostbyname() and gethostbyaddr() functions return
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the hostent structure or a NULL pointer if an error
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the hostent structure or a NULL pointer if an error
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occurs. On error, the h_errno variable holds an error
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occurs. On error, the h_errno variable holds an error
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number.
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number.
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ERRORS
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ERRORS
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The variable h_errno can have the following values:
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The variable h_errno can have the following values:
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HOST_NOT_FOUND
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HOST_NOT_FOUND
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The specified host is unknown.
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The specified host is unknown.
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NO_ADDRESS or NO_DATA
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NO_ADDRESS or NO_DATA
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The requested name is valid but does not have an IP
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The requested name is valid but does not have an IP
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address.
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address.
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NO_RECOVERY
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NO_RECOVERY
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A non-recoverable name server error occurred.
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A non-recoverable name server error occurred.
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TRY_AGAIN
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TRY_AGAIN
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A temporary error occurred on an authoritative name
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A temporary error occurred on an authoritative name
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server. Try again later.
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server. Try again later.
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