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An Internet host name to address mapping is represented by the hostent structure:
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type (for example, AF_INET) */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses, null terminated */
};
#define h_addr h_addr_list[0] /* first address, network byte order */
The routine
gethostbyname
takes an Internet host name
and returns a
hostent
structure,
while the routine
gethostbyaddr
maps Internet host addresses into a
hostent
structure.
These two routines are described on the
gethostent(3N)
manual page.
The routine
inet_ntoa
maps an Internet host address into an
ASCII
string for printing by
log and error messages.
This function is described on the
inet(3N)
manual page.
The official name of the host and its public aliases are returned by these routines, along with the address type (domain) and a null terminated list of variable length addresses. This list of addresses is required because it is possible for a host to have many addresses, all having the same name. The h_addr definition is provided for backward compatibility, and is defined to be the first address in the list of addresses in the hostent structure.