cc [ flag ... ] file ... –lxnet [ library ... ] #include <netdb.h> extern int h_errno; void endhostent(void)
struct hostent *gethostbyaddr(const void *addr, socklen_t len, int type);
struct hostent *gethostbyname(const char *name);
struct hostent *gethostent(void)
void sethostent(int stayopen);
The gethostent(), gethostbyaddr(), and gethostbyname() functions each return a pointer to a hostent structure, the members of which contain the fields of an entry in the network host database.
The gethostent() function reads the next entry of the database, opening a connection to the database if necessary.
The gethostbyaddr() function searches the database and finds an entry which matches the address family specified by the type argument and which matches the address pointed to by the addr argument, opening a connection to the database if necessary. The addr argument is a pointer to the binary-format (that is, not null-terminated) address in network byte order, whose length is specified by the len argument. The datatype of the address depends on the address family. For an address of type AF_INET, this is an in_addr structure, defined in <netinet/in.h>. For an address of type AF_INET6, there is an in6_addr structure defined in < netinet/in.h>.
The gethostbyname() function searches the database and finds an entry which matches the host name specified by the name argument, opening a connection to the database if necessary. If name is an alias for a valid host name, the function returns information about the host name to which the alias refers, and name is included in the list of aliases returned.
The sethostent() function opens a connection to the network host database, and sets the position of the next entry to the first entry. If the stayopen argument is non-zero, the connection to the host database will not be closed after each call to gethostent() (either directly, or indirectly through one of the other gethost*( ) functions).
The endhostent() function closes the connection to the database.
The gethostent(), gethostbyaddr(), and gethostbyname() functions may return pointers to static data, which may be overwritten by subsequent calls to any of these functions.
These functions are generally used with the Internet address family.
On successful completion, gethostbyaddr(), gethostbyname() and gethostent() return a pointer to a hostent structure if the requested entry was found, and a null pointer if the end of the database was reached or the requested entry was not found. Otherwise, a null pointer is returned.
On unsuccessful completion, gethostbyaddr() and gethostbyname() functions set h_errno to indicate the error.
No errors are defined for endhostent(), gethostent() and sethostent().
The gethostbyaddr() and gethostbyname() functions will fail in the following cases, setting h_errno to the value shown in the list below. Any changes to errno are unspecified.
No such host is known.
The server recognised the request and the name but no address is available. Another type of request to the name server for the domain might return an answer.
An unexpected server failure occurred which can not be recovered.
A temporary and possibly transient error occurred, such as a failure of a server to respond.
See attributes(5) for descriptions of the following attributes: