我编写或修改执行名称解析的程序并需要
过程控制良好。 所以我不使用getaddrinfo()，我去
更深入并在 resolv.h 中使用 res_query() / res_send() / 等，已记录
在解析器(3)中。
尽管没有记录，但设置解析器的常用方法是
更新_res.nsaddr_list。 但是这个数组，在 resolv.h 中定义，存储
struct sockaddr_in，仅是 IPv4 地址。 （IPv6 地址
是 struct sockaddr_in6 ，独立于系列的系统将使用 struct sockaddr 。）
我正在寻找一种方法（最好是可移植的，至少在
各种 Unix）告诉 _res 我也想要 IPv6 地址。
显然，很久以前，FreeBSD 中有一个 _res_ext 与此
能力，但我在最近的 FreeBSD 7 中找不到它了（grep
_res_ext /usr/include/resolv.h 找不到任何内容）。 你仍然可以找到
使用它的代码（自己尝试使用 Google Codesearch ）。
感谢 Alnitak，我注意到它现在显然是 _res._ext 而不是 .res_ext。 我想知道这些事情在哪里记录或宣布...我不知道 _res._ext 的可移植性如何。 我可以在 Debian 和 FreeBSD 上找到它。 似乎很少有程序使用它。
I write or modify programs which perform name resolution and need a
good control of the process. So I do not use getaddrinfo(), I go
deeper and use res_query() / res_send() / etc in resolv.h, documented
in resolver(3).
Although not documented, the common way to set the resolver used is to
update _res.nsaddr_list. But this array, defined in resolv.h, stores
struct sockaddr_in, that is IPv4 addresses only. (IPv6 addresses
are struct sockaddr_in6, a family-independant system would use struct sockaddr.)
I'm looking for a way (preferrably portable, at least among the
various Unix) to tell _res that I want also IPv6 addresses.
Apparently, a long time ago, there was in FreeBSD a _res_ext with this
ability but I cannot find it anymore in a recent FreeBSD 7 (grep
_res_ext /usr/include/resolv.h finds nothing). You can still find
code which uses it (try yourself with Google Codesearch).
Thanks to Alnitak, I noticed it is apparently now _res._ext and not .res_ext. I wonder where these sort of things are documented or announced... I have no idea how portable _res._ext is. I can find it on Debian and FreeBSD. It seems there are few programs which use it.
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Stéphane - 如果您的
resolv.h不包含对sockaddr_in6的任何支持，那么这表明在您的特定操作系统上，解析器本身不支持 IPv6 传输。我在这里检查了我的一些系统：
MacOS X 10.5.6 - 支持 BIND 9 库，该库具有
res_setservers()函数，可以采用 IPv6地址，无_res._ext扩展名。CentOS 5.2 - 具有
_res._ext扩展名，尽管resolv.conf的手册页中没有提及 IPv6，只是有一个设置告诉解析器在查找gethostbyname()的 A 记录之前返回 AAAA 记录。编辑 - 另外，FreeBSD 的 CVS 存储库 建议FreeBSD 7.0（请参阅标记
FREEBSD_7_0_0_RELEASE）也支持 Bind 9 中的res_setservers()。Stéphane - if your
resolv.hdoesn't include any support forsockaddr_in6then that suggests that on your particular O/S the resolver does not itself support IPv6 transport.I've checked some of my systems here:
MacOS X 10.5.6 - supports the BIND 9 library, which has a
res_setservers()function which can take IPv6 addresses, no_res._extextension.CentOS 5.2 - has the
_res._extextension, although there's no mention of IPv6 in the man page forresolv.confexcept that there's a setting to tell the resolver to return AAAA records before looking for A records forgethostbyname().EDIT - also, the CVS repository for FreeBSD suggests that FreeBSD 7.0 (see tag
FREEBSD_7_0_0_RELEASE) does also supportres_setservers()from Bind 9.glibc：
根据以下内容将后者设置为 MAXNS+1：
http:// sourceware.org/ml/libc-hacker/2002-05/msg00035.html
BSD-libc：
对我来说似乎很混乱，您可能需要 autoconf。
glibc:
set the latter to MAXNS+1 according to:
http://sourceware.org/ml/libc-hacker/2002-05/msg00035.html
BSD-libc:
Seems messy to me and you'll probably need autoconf.