Networking Services Library Functions gethostbyname(3NSL)
NAME
gethostbyname, gethostbyname_r, gethostbyaddr,
gethostbyaddr_r, gethostent, gethostent_r, sethostent,
endhostent - get network host entry
SYNOPSIS
cc [ flag... ] file... -lnsl [ library... ]
#include
struct hostent *gethostbyname(const char *name);struct hostent *gethostbyname_r(const char *name,
struct hostent *result, char *buffer, int buflen,int *h_errnop);
struct hostent *gethostbyaddr(const char *addr, int len, int type);struct hostent *gethostbyaddr_r(const char *addr, int length,
int type, struct hostent *result, char *buffer,int buflen, int *h_errnop);
struct hostent *gethostent(void);
struct hostent *gethostent_r(struct hostent *result,
char *buffer, int buflen, int *h_errnop);
int sethostent(int stayopen); int endhostent(void);DESCRIPTION
These functions are used to obtain entries describing hosts.An entry can come from any of the sources for hosts speci-
fied in the /etc/nsswitch.conf file. See nsswitch.conf(4). These functions have been superseded by getipnodebyname(3SOCKET), getipnodebyaddr(3SOCKET), and getaddrinfo(3SOCKET), which provide greater portability toapplications when multithreading is performed or technolo-
gies such as IPv6 are used. For example, the functions described in the following cannot be used with applications targeted to work with IPv6.SunOS 5.11 Last change: 30 Mar 2010 1
Networking Services Library Functions gethostbyname(3NSL) The gethostbyname() function searches for information for ahost with the hostname specified by the character-string
parameter name. The gethostbyaddr() function searches for information for a host with a given host address. The parameter type specifies the family of the address. This should be one of the address families defined in. See the NOTES section for more information. Also see the EXAMPLES section for
information on how to convert an Internet IP address nota-
tion that is separated by periods (.) into an addr parame-
ter. The parameter len specifies the length of the buffer indicated by addr. All addresses are returned in network order. In order to interpret the addresses, byteorder(3SOCKET) must be used for byte order conversion.The sethostent(), gethostent(), and endhostent() functions
are used to enumerate host entries from the database. The sethostent() function sets or resets the enumeration to the beginning of the set of host entries. This functionshould be called before the first call to gethostent().
Calls to gethostbyname() and gethostbyaddr() leave theenumeration position in an indeterminate state. If the stay-
open flag is non-zero, the system can keep allocated
resources such as open file descriptors until a subsequent call to endhostent().Successive calls to the gethostent() function return either
successive entries or NULL, indicating the end of the enumeration. The endhostent() function can be called to indicate that thecaller expects to do no further host entry retrieval opera-
tions; the system can then deallocate resources it was using. It is still allowed, but possibly less efficient, forthe process to call more host retrieval functions after cal-
ling endhostent(). Reentrant InterfacesThe gethostbyname(), gethostbyaddr(), and gethostent() func-
tions use static storage that is reused in each call, makingthese functions unsafe for use in multithreaded applica-
tions.SunOS 5.11 Last change: 30 Mar 2010 2
Networking Services Library Functions gethostbyname(3NSL)The gethostbyname_r(), gethostbyaddr_r(), and gethostent_r()
functions provide reentrant interfaces for these operations. Each reentrant interface performs the same operation as itsnon-reentrant counterpart, named by removing the _r suffix.
The reentrant interfaces, however, use buffers supplied by the caller to store returned results and the interfaces aresafe for use in both single-threaded and multithreaded
applications. Each reentrant interface takes the same parameters as itsnon-reentrant counterpart, as well as the following addi-
tional parameters. The parameter result must be a pointer toa struct hostent structure allocated by the caller. On suc-
cessful completion, the function returns the host entry in this structure. The parameter buffer must be a pointer to a buffer supplied by the caller. This buffer is used as storage space for the host data. All of the pointers within the returned struct hostent result point to data storedwithin this buffer. See the RETURN VALUES section for more
information. The buffer must be large enough to hold all of the data associated with the host entry. The parameter buflen should give the size in bytes of the buffer indicatedby buffer. The parameter h_errnop should be a pointer to an
integer. An integer error status value is stored there oncertain error conditions. See the ERRORS section for more
information. For enumeration in multithreaded applications, the positionwithin the enumeration is a process-wide property shared by
all threads. The sethostent() function can be used in a mul-
tithreaded application but resets the enumeration position for all threads. If multiple threads interleave calls togethostent_r(), the threads will enumerate disjoint subsets
of the host database.Like their non-reentrant counterparts, gethostbyname_r() and
gethostbyaddr_r() leave the enumeration position in an
indeterminate state.RETURN VALUES
Host entries are represented by the struct hostent structure defined in: struct hostent { char *h_name; /* canonical name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
SunOS 5.11 Last change: 30 Mar 2010 3
Networking Services Library Functions gethostbyname(3NSL)int h_length; /* length of address */
char **h_addr_list; /* list of addresses */
};See the EXAMPLES section for information about how to
retrieve a ``.'' separated Internet IP address string fromthe h_addr_list field of struct hostent.
The gethostbyname(), gethostbyname_r(), gethostbyaddr(), and
gethostbyaddr_r() functions each return a pointer to a
struct hostent if they successfully locate the requested entry; otherwise they return NULL.The gethostent() and gethostent_r() functions each return a
pointer to a struct hostent if they successfully enumerate an entry; otherwise they return NULL, indicating the end of the enumeration.The gethostbyname(), gethostbyaddr(), and gethostent() func-
tions use static storage, so returned data must be copied before a subsequent call to any of these functions if the data is to be saved. When the pointer returned by the reentrant functionsgethostbyname_r(), gethostbyaddr_r(), and gethostent_r() is
not NULL, it is always equal to the result pointer that was supplied by the caller.The sethostent() and endhostent() functions return 0 on suc-
cess.ERRORS
The reentrant functions gethostbyname_r(),
gethostbyaddr_r(), and gethostent_r() will return NULL and
set errno to ERANGE if the length of the buffer supplied by caller is not large enough to store the result. See Intro(2)for the proper usage and interpretation of errno in mul-
tithreaded applications.The reentrant functions gethostbyname_r() and
gethostbyaddr_r() set the integer pointed to by h_errnop to
one of these values in case of error.SunOS 5.11 Last change: 30 Mar 2010 4
Networking Services Library Functions gethostbyname(3NSL)On failures, the non-reentrant functions gethostbyname() and
gethostbyaddr() set a global integer h_errno to indicate one
of these error codes (defined in
): HOST_NOT_FOUND, TRY_AGAIN, NO_RECOVERY, NO_DATA, and NO_ADDRESS.
If a resolver is provided with a malformed address, or if any other error occurs before gethostbyname() is resolved, then gethostbyname() returns an internal error with a valueof -1.
The gethostbyname() function will set h_errno to
NETDB_INTERNAL when it returns a NULL value.
EXAMPLES
Example 1 Using gethostbyaddr() Here is a sample program that gets the canonical name, aliases, and ``.'' separated Internet IP addresses for a given ``.'' separated IP address:#include
#include
#include
#include
#include
#include
#include
#include
int main(int argc, const char **argv) {in_addr_t addr;
struct hostent *hp; char **p; if (argc != 2) {(void) printf("usage: %s IP-address\n", argv[0]);
exit (1); }if ((int)(addr = inet_addr(argv[1])) == -1) {
(void) printf("IP-address must be of the form a.b.c.d\n");
exit (2); }hp = gethostbyaddr((char *)&addr, 4, AF_INET);
if (hp == NULL) {(void) printf("host information for %s not found\n", argv[1]);
exit (3); }for (p = hp->h_addr_list; *p != 0; p++) {
struct in_addr in;
SunOS 5.11 Last change: 30 Mar 2010 5
Networking Services Library Functions gethostbyname(3NSL) char **q;(void) memcpy(&in.s_addr, *p, sizeof (in.s_addr));
(void) printf("%s%s", inet_ntoa(in), hp->h_name);
for (q = hp->h_aliases; *q != 0; q++)
(void) printf(" %s", *q);
(void) putchar('0); } exit (0); } Note that the preceding sample program is unsafe for use in multithreaded applications. FILES /etc/hosts hosts file that associates the names of hosts with their Internet Protocol (IP) addresses /etc/netconfig network configuration database/etc/nsswitch.conf configuration file for the name ser-
vice switchATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| ____________________________|_____________________________|_
| MT-Level | See Reentrant Interfaces in|
| | the DESCRIPTION section. |
|_____________________________|_____________________________|
SEE ALSO
Intro(2), Intro(3), byteorder(3SOCKET), inet(3SOCKET), netdb.h(3HEAD), netdir(3NSL), hosts(4), netconfig(4), nss(4), nsswitch.conf(4), attributes(5) WARNINGSThe reentrant interfaces gethostbyname_r(),
gethostbyaddr_r(), and gethostent_r() are included in this
release on an uncommitted basis only and are subject toSunOS 5.11 Last change: 30 Mar 2010 6
Networking Services Library Functions gethostbyname(3NSL) change or removal in future minor releases. NOTESTo ensure that they all return consistent results, gethost-
byname(), gethostbyname_r(), and netdir_getbyname() are
implemented in terms of the same internal library function.This function obtains the system-wide source lookup policy
based on the inet family entries in netconfig(4) and thehosts: entry in nsswitch.conf(4). Similarly, gethost-
byaddr(), gethostbyaddr_r(), and netdir_getbyaddr() are
implemented in terms of the same internal library function.If the inet family entries in netconfig(4) have a ``-'' in
the last column for nametoaddr libraries, then the entry for hosts in nsswitch.conf will be used; nametoaddr libraries inthat column will be used, and nsswitch.conf will not be con-
sulted.There is no analogue of gethostent() and gethostent_r() in
the netdir functions, so these enumeration functions gostraight to the hosts entry in nsswitch.conf. Thus enumera-
tion can return results from a different source than thatused by gethostbyname(), gethostbyname_r(), gethostbyaddr(),
and gethostbyaddr_r().
All the functions that return a struct hostent must alwaysreturn the canonical name in the h_name field. This name, by
definition, is the well-known and official hostname shared
between all aliases and all addresses. The underlying source that satisfies the request determines the mapping of the input name or address into the set of names and addresses in hostent. Different sources might do that in different ways. If there is more than one alias and more than one address in hostent, no pairing is implied between them. The system attempts to put those addresses that are on thesame subnet as the caller before addresses that are on dif-
ferent subnets. However, if address sorting is disabled bysetting SORT_ADDRS to FALSE in the /etc/default/nss file,
the system does not put the local subnet addresses first. See nss(4) for more information. When compiling multithreaded applications, see Intro(3), MULTITHREADED APPLICATIONS, for information about the use ofthe _REENTRANT flag.
Use of the enumeration interfaces gethostent() and
gethostent_r() is discouraged; enumeration might not be
SunOS 5.11 Last change: 30 Mar 2010 7
Networking Services Library Functions gethostbyname(3NSL) supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(4). The current implementations of these functions only return or accept addresses for the Internet address family (typeAF_INET).
The form for an address of type AF_INET is a struct in_addr
defined in. The functions described in inet(3SOCKET), and illustrated in the EXAMPLES section, are
helpful in constructing and manipulating addresses in this form. When the caller provides the IP address (the addr argumentof gethostbyaddr() and gethostbyaddr_r()), the addr argument
should be aligned on a word boundary or the code must bechanged to memcpy(3C) the argument to an aligned area; oth-
erwise an error such as a SIGBUS may result.SunOS 5.11 Last change: 30 Mar 2010 8