How might I perform DNS lookups using C/C++ on Lin

问题:

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.

回答1:

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));

回答2:

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

回答3:

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.

回答4:

I like adns because it allows for asynchronous requests

回答5:

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.

回答6:

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

回答7:

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)