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

Question

How do I get similar functionality to the host command using ac 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.

Answer 1

如果阻塞（同步）查询没问题，则只需使用res_query() ，然后将程序与-lresolv链接即可。

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

Answer 2

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

Answer 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.

Answer 4

我喜欢adns，因为它允许异步请求

Answer 5

而且我要补充一点，除非您正在编写邮件中继，否则几乎可以肯定不应该查找MX记录-您应该将邮件传递给用户配置的邮件中继。

Answer 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

Answer 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)