res_query()

The res_query() call provides an interface to the server query mechanism.

Syntax

#include <sys\types.h>
#include <netinet\in.h>
#include <arpa\nameser.h>
#include <resolv.h>
int res_query(name, class, type, answer, anslen)
char *name;
int class;
int type;
u_char *answer;
int anslen;

Parameters

name

Points to the name of the domain. If the name parameter points to a single-component name and the RES_DEFNAMES structure is set, as it is by default, the call 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 file.

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.
anslen
Specifies the size of the answer buffer.

Description

The res_query() call 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 name parameter. The reply message is left in the answer buffer whose size is specified by the anslen parameter, which is supplied by the caller.

The caller must parse answer and determine whether it answers the question.

The res_query() call is one of a group of calls that form the resolver, a set of functions that resolve domain names. The _res data structure contains global information used by the resolver calls. The <RESOLV.H> file contains the _res structure definition. (See The _res Data Structure for more on the _res data structure.)

Return Values

When successful, the res_query() call returns the size of the response. When unsuccessful, the res_query() call returns a value of -1 and sets the h_errno value to the appropriate error.

Related Calls

dn_comp() dn_expand()
dn_find()
dn_skipname()


• getlong()
  
• getshort()
  putlong()
  putshort()
  res_init()
  res_mkquery()
  res_search()
  res_send()

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