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AIX Version 4.3 Communications Technical Reference, Volume 2

res_query Subroutine


Provides an interface to the server query mechanism.


Standard C Library (libc.a)


#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
int res_query (DomName, Class, Type, Answer, AnswerLength)
char *DomName;
int Class;
int Type;
u_char *Answer;
int AnswerLength;


The res_query subroutine provides an interface to the server query mechanism. It constructs a query, sends it to the local server, awaits a response, and makes preliminary checks on the reply. The query requests information of the specified type and class for the fully-qualified domain name specified in the DomName parameter. The reply message is left in the answer buffer whose size is specified by the AnswerLength parameter, which is supplied by the caller.

The res_query subroutine is one of a set of subroutines that form the resolver, a set of functions that resolve domain names. The _res data structure contains global information used by the resolver subroutines. The /usr/include/resolv.h file contains the _res structure definition.


DomName Points to the name of the domain. If the DomName parameter points to a single-component name and the RES_DEFNAMES structure is set, as it is by default, the subroutine appends the default domain name to the single-component name. The current domain name is defined by the name server in use or is specified in the /etc/resolv.conf file.
Class Specifies one of the following values:
C_IN Specifies the ARPA Internet.
C_CHAOS Specifies the Chaos network at MIT.
Type Requires one of the following values:
T_A Host address
T_NS Authoritative server
T_MD Mail destination
T_MF Mail forwarder
T_CNAME Canonical name
T_SOA Start-of-authority zone
T_MB Mailbox-domain name
T_MG Mail-group member
T_MR Mail-rename name
T_NULL Null resource record
T_WKS Well-known service
T_PTR Domain name pointer
T_HINFO Host information
T_MINFO Mailbox information
T_MX Mail-routing information
T_UINFO User (finger command) information
T_GID Group ID
Answer Points to an address where the response is stored.
AnswerLength Specifies the size of the answer buffer.

Return Values

Upon successful completion, the res_query subroutine returns the size of the response. Upon unsuccessful completion, the res_query subroutine returns a value of -1 and sets the h_errno value to the appropriate error.

Implementation Specifics

The res_query subroutine is part of Base Operating System (BOS) Runtime.

All applications containing the res_query subroutine must be compiled with _BSD set to a specific value. Acceptable values are 43 and 44. In addition, all socket applications must include the BSD libbsd.a library.


                          Contains the name server and domain name.

Related Information

The finger command.

The dn_comp subroutine, dn_expand subroutine, _getlong subroutine, _getshort subroutine, putlong subroutine, putshort subroutine, res_init subroutine, res_mkquery subroutine, res_search subroutine, res_send subroutine.

Sockets Overview and Understanding Domain Name Resolution in AIX Version 4.3 Communications Programming Concepts.

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