GETHOSTBYADDR(P) POSIX Programmer's Manual GETHOSTBYADDR(P)
NAME
gethostbyaddr, gethostbyname - network host database functions
SYNOPSIS
#include <netdb.h>
struct hostent *gethostbyaddr(const void *addr, socklen_t len,
int type);
struct hostent *gethostbyname(const char *name);
DESCRIPTION
These functions shall retrieve information about hosts. This information is considered to be stored in a database that can be accessed
sequentially or randomly. Implementation of this database is unspecified.
Note: In many cases it is implemented by the Domain Name System, as documented in RFC 1034, RFC 1035, and RFC 1886.
Entries shall be returned in hostent structures.
The gethostbyaddr() function shall return an entry containing addresses of address family type for the host with address addr. The len
argument contains the length of the address pointed to by addr. The gethostbyaddr() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
The gethostbyname() function shall return an entry containing addresses of address family AF_INET for the host with name name. The gethost-
byname() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.
The addr argument of gethostbyaddr() shall be an in_addr structure when type is AF_INET. It contains a binary format (that is, not null-
terminated) address in network byte order. The gethostbyaddr() function is not guaranteed to return addresses of address families other
than AF_INET, even when such addresses exist in the database.
If gethostbyaddr() returns successfully, then the h_addrtype field in the result shall be the same as the type argument that was passed to
the function, and the h_addr_list field shall list a single address that is a copy of the addr argument that was passed to the function.
The name argument of gethostbyname() shall be a node name; the behavior of gethostbyname() when passed a numeric address string is unspeci-
fied. For IPv4, a numeric address string shall be in the dotted-decimal notation described in inet_addr() .
If name is not a numeric address string and is an alias for a valid host name, then gethostbyname() shall return information about the host
name to which the alias refers, and name shall be included in the list of aliases returned.
RETURN VALUE
Upon successful completion, these functions shall 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.
Upon unsuccessful completion, gethostbyaddr() and gethostbyname() shall set h_errno to indicate the error.
ERRORS
These functions shall fail in the following cases. The gethostbyaddr() and gethostbyname() functions shall set h_errno to the value shown
in the list below. Any changes to errno are unspecified.
HOST_NOT_FOUND
No such host is known.
NO_DATA
The server recognized 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.
NO_RECOVERY
An unexpected server failure occurred which cannot be recovered.
TRY_AGAIN
A temporary and possibly transient error occurred, such as a failure of a server to respond.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The gethostbyaddr() and gethostbyname() functions may return pointers to static data, which may be overwritten by subsequent calls to any
of these functions.
The getaddrinfo() and getnameinfo() functions are preferred over the gethostbyaddr() and gethostbyname() functions.
RATIONALE
None.
FUTURE DIRECTIONS
The gethostbyaddr() and gethostbyname() functions may be withdrawn in a future version.
SEE ALSO
endhostent() , endservent() , gai_strerror() , getaddrinfo() , h_errno() , inet_addr() , the Base Definitions volume of
IEEE Std 1003.1-2001, <netdb.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE
/The Open Group 2003 GETHOSTBYADDR(P)