iOS dns PTR record query

gistfile1.m

#include <dns_sd.h>
#include <resolv.h>
void DNSSD_API callback
(
 DNSServiceRef sdRef,
 DNSServiceFlags flags,
 uint32_t interfaceIndex,
 DNSServiceErrorType errorCode,
 const char                          *fullname,
 uint16_t rrtype,
 uint16_t rrclass,
 uint16_t rdlen,
 const void                          *rdata,
 uint32_t ttl,
 void                                *context
 );

void DNSSD_API callback
(
 DNSServiceRef sdRef,
 DNSServiceFlags flags,
 uint32_t interfaceIndex,
 DNSServiceErrorType errorCode,
 const char                          *fullname,
 uint16_t rrtype,
 uint16_t rrclass,
 uint16_t rdlen,
 const void                          *rdata,
 uint32_t ttl,
 void                                *context
 )
{
    NSLog(@"queryCallback: flags == %d error code == %d", flags, errorCode);
    
    char result[256]={0};
    //memcpy(result, rdata, rdlen);
    //NSString *a=[[NSString alloc] initWithBytes:rdata length:rdlen encoding:NSUTF8StringEncoding];
    
    dn_expand(rdata, rdata + rdlen, rdata, result, 256);
    NSLog(@"result %s",result);
}

int test()
{
    DNSServiceRef sdRef;
    DNSServiceErrorType res;
    
    res=DNSServiceQueryRecord(
                              &sdRef, 0, 0,
                              "1.18.168.192.in-addr.arpa.",
                              kDNSServiceType_PTR,
                              kDNSServiceClass_IN,
                              callback,
                              NULL
                              );
    
    DNSServiceProcessResult(sdRef);
    DNSServiceRefDeallocate(sdRef);
    return 0;
}