gethostent.3n (2010 09)

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gethostent(3N) gethostent(3N)
gethostent() Always returns a NULL pointer.
sethostent() Requests the use of a connected stream socket for queries to the name
server if the stayopen flag is non-zero. The connection is retained after
each call to gethostbyname()
or gethostbyaddr()
.
endhostent() Closes the stream socket connection.
gethostbyname()
gethostbyaddr()
Each retrieves host information from the name server. Names are matched
without respect to uppercase or lowercase. For example,
berkeley.edu,
Berkeley.EDU, and BERKELEY.EDU all match the entry for
berkeley.edu.
NIS Server Operation
If
ypserv, the server for the Network Information Service (see ypserv (1M)), is used for name or address
resolution, then the function:
gethostent() Returns the next entry in the NIS database.
sethostent() Initializes an internal key for the NIS database. If the stayopen flag is
non-zero, the internal key is not cleared after calls to
endhostent().
endhostent() Clears the internal NIS database key.
gethostbyname()
gethostbyaddr() Each retrieves host information from the NIS database. Names are
matched without respect to uppercase or lowercase. For example,
berkeley.edu, Berkeley.EDU, and BERKELEY.EDU all match the
entry for berkeley.edu.
Nonserver Operation
If the
/etc/hosts file is used for name or address resolution, then the function:
gethostent() Reads the next line of /etc/hosts, opening the file if necessary.
sethostent() Opens and rewinds the file. If the stayopen flag is non-zero, the host data
base is not closed after each call to gethostent() (either directly or
indirectly through one of the other gethost calls).
endhostent() Closes the file.
gethostbyname() Sequentially searches from the beginning of the file until a host name
(among either the official names or the aliases) matching its name parame-
ter is found, or until EOF is encountered. Names are matched without
respect to uppercase or lowercase, as described above in the name server
case.
gethostbyaddr() Sequentially searches from the beginning of the file until an Internet
address matching its addr parameter is found, or until EOF is encoun-
tered.
The return value,
struct hostent, must be saved before a subsequent call to the functions
gethost*(), getaddrinfo(), and getnameinfo().
In a multithreaded application,
gethostent(), gethostbyaddr(), and
gethostbyname() use
thread-specific storage that is re-used in each call. The return value,
struct hostent, should be
unique for each thread and should be saved, if desired, before the thread makes the next gethost*()
call. The return value must be saved before a subsequent call to the function getaddrinfo() or get-
nameinfo(), because these functions may internally call the gethost*() function which may
overwrite their return value.
For enumeration in multithreaded applications, the position within the enumeration is a process-wide
property shared by all threads.
sethostent() may be used in a multithreaded application, but resets
the enumeration position for all threads. If multiple threads interleave calls to gethostent(), the
threads will enumerate disjoint subsets of the host database.
Arguments
Currently, only the Internet address format is understood. In calls to
gethostbyaddr(), the parame-
ter addr must be a pointer to an in_addr structure, an Internet address in network order (see
2 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: September 2010