gethostbyname()或getnameinfo()在后台如何工作?

本文介绍了gethostbyname()或getnameinfo()在后台如何工作?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

gethostbyname()或 getnameinfo()在后台如何工作?

How gethostbyname() or getnameinfo() work in background?

#include <stdlib.h> #include <stdio.h> #include <netdb.h> /* paddr: print the IP address in a standard decimal dotted format */ void paddr(unsigned char *a) { printf("%d.%d.%d.%d\n", a[0], a[1], a[2], a[3]); } main(int argc, char **argv) { struct hostent *hp; char *host = "google"; int i; hp = gethostbyname(host); if (!hp) { fprintf(stderr, "could not obtain address of %s\n", host); return 0; } for (i=0; hp->h_addr_list[i] != 0; i++) paddr((unsigned char*) hp->h_addr_list[i]); exit(0); }

google的输出:

output for google:

74.125.236.198 74.125.236.199 74.125.236.206 74.125.236.201 74.125.236.200 74.125.236.196 74.125.236.193 74.125.236.197 74.125.236.194 74.125.236.195 74.125.236.192

www.google的输出:

output for www.google:

74.125.236.210 74.125.236.209 74.125.236.212 74.125.236.208 74.125.236.211

上述程序会在互联网上进行检查以解析为IP吗?

为什么显示 www.google 的IP地址较少，而仅仅显示 google 的IP地址较多?

Will the above program do a check in the internet to resolve into IP?

Why its showing less IP addresses for www.google and more for just google?

推荐答案

在Linux系统上，在glibc中实现的gethostbyname()调用根据配置文件/etc/host.conf 执行查找.和/etc/nsswitch.conf .

On a Linux system the gethostbyname() call implemented in the glibc performs lookups according to the configuration files /etc/host.conf and /etc/nsswitch.conf.

通常，在默认配置中，如果存在给定名称的本地条目，则它将首先在/etc/hosts 文件中查找，如果存在，则返回该名称.否则，它将继续使用由/etc/resolv.conf 配置的DNS协议，其中指定了名称服务器.

Typically in a default configuration it will first look in the /etc/hosts file if a local entry for the given name exists and if so, returns that. Otherwise it will proceed with the DNS protocol that is in turn configured by /etc/resolv.conf where the nameservers are stated.

可以配置更多复杂的设置来查找LDAP服务器，数据库等.

Much more complex setups can be configured that lookup LDAP servers, databases etc.

您还可以查看一些手册页，例如 man 5 nsswitch.conf .

You can also look into some man pages like man 5 nsswitch.conf.