GETHOSTBYNAME(3) | Library Functions Manual | GETHOSTBYNAME(3) |
extern int h_errno;
struct hostent *
gethostbyname(const char *name);
struct hostent *
gethostbyname2(const char *name, int af);
struct hostent *
gethostbyaddr(const char *addr, socklen_t len, int type);
struct hostent *
gethostent(void);
void
sethostent(int stayopen);
void
endhostent(void);
void
herror(const char *string);
const char *
hstrerror(int err);
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:
In the case of gethostbyname() and gethostbyname2(), the host is specified by name, or using a string representation of a numeric address. In the case of gethostbyaddr(), the host is specified using a binary representation of an address.
The returned struct hostent structure may contain the result of a simple string to binary conversion, information obtained from the domain name resolver (see resolver(3)), broken-out fields from a line in /etc/hosts, or database entries supplied by the yp(8) system. The order of the lookups is controlled by the ‘hosts' entry in nsswitch.conf(5).
When using the domain name resolver, gethostbyname() and gethostbyname2() 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 hostname(7) for the domain search procedure and the alias file format.
The gethostbyname2() function is an evolution of gethostbyname() which is intended to allow lookups in address families other than AF_INET, for example AF_INET6. Currently the af argument must be specified as AF_INET or AF_INET6, else the function will return NULL after having set h_errno to NETDB_INTERNAL.
The gethostent() function reads the next line of the /etc/hosts file, opening the file if necessary.
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(), gethostbyname2(), or gethostbyaddr(). Otherwise, queries are performed using UDP datagrams.
The endhostent() function closes the TCP connection.
The herror() function writes a message to the diagnostic output consisting of the string parameter s, the constant string ": ", and a message corresponding to the value of h_errno.
The hstrerror() function returns a string which is the message text corresponding to the value of the err parameter.
The variable h_errno can have the following values:
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(), gethostbyaddr(), or gethostent().
The endhostent() function closes the file.
The gethostent() does not currently follow the search order specified in nsswitch.conf(5) and only reads the /etc/hosts file.
October 7, 2006 | NetBSD 6.1 |