How might I perform DNS lookups using C/C++ on Linux?

Question

How do I get similar functionality to the host command using a c api (or any other language for that matter)? I need more information than just an IP address given by gethostbyname(); specifically, the SMTP-related data.

When you mention *smtp-related*, do you mean the MX record for a domain? — DaveR, Jul 14 '09 at 22:32
duplicate of http://stackoverflow.com/questions/1093410/pulling-mx-record-from-dns-server and several otehrs — Alnitak, Jul 15 '09 at 13:30

score 21 · Accepted Answer · answered Jul 15 '09 at 04:49

21

If a blocking (synchronous) query is ok, just use res_query(), and link your program with -lresolv.

 len = res_query(host, C_IN, T_MX, &answer, sizeof(answer));

answered Jul 15 '09 at 04:49

mark4o

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score 1 · Answer 2 · answered Jul 14 '09 at 22:51

1

I'd suggest FireDNS. It's a very fast C library for all kinds of dns queries.

answered Jul 14 '09 at 22:51

ko-dos

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The project looks abandonned (last release in 2004) and unfortunately the download link doesn't work (http://www.firestuff.org/)... – Destroyica Mar 29 '12 at 08:09

score 1 · Answer 3 · answered Jul 13 '12 at 10:28

I know that the question is old, but I have long searched a dns library, and all answers here just stubs me. I think libraries like adns/udns have written not for human beings. And FireDNS for a long time have not working download links.

I have found poslib as the best dns library with very easy interface.

score 1 · Answer 4 · edited Nov 04 '12 at 21:36

1

I like adns because it allows for asynchronous requests

edited Nov 04 '12 at 21:36

yfrancis

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answered Dec 09 '11 at 06:29

Finaldie

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ps, I prefer like the FireDns, because it much easier and clearer :D – Finaldie Dec 11 '11 at 01:50

DaveR · Answer 5 · 2009-07-14T22:51:36.847

I don't think there is a function in the C standard library for this, but many scripting languages do have this functionality 'built in'. For example, Perl has the Net::DNS package:

use Net::DNS;
my @mx = mx("example.com");
foreach $host (@mx) {
  print $host;
}

If you need to do this in C, a quick google shows up a few C libraries out there which you can use:

adns
udns
dns.c
FireDNS (as mentioned by ko-dos)

score 0 · Answer 6 · answered Jul 15 '09 at 07:38

0

And I would add, unless you're writing a mail relay you almost certainly shouldn't be looking up MX records - you should be passing the mail on to a user-configured mail relay instead.

answered Jul 15 '09 at 07:38

caf

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score 0 · Answer 7 · answered Oct 22 '18 at 11:03

0

You can also try c-ares library https://c-ares.haxx.se/, which allows to send asynchronous DNS queries. It also comes with adig - its own version of dig utility for querying DNS. You can check it to see how to parse DNS reply: adig.c source

answered Oct 22 '18 at 11:03

Daniel Frużyński

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How might I perform DNS lookups using C/C++ on Linux?

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