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Technical Reference: Communications, Volume 2


res_query Subroutine

Purpose

Provides an interface to the server query mechanism.

Library

Standard C Library (libc.a)

Syntax

#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;

Description

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.

Parameters


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_UID
User ID

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.

Files


/etc/resolv.conf
                          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 5L Version 5.1 Communications Programming Concepts.


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