Linux:通过域名，获取IP地址函数使用 Linux

Linux:通过域名,获取IP地址

参考链接：
https://blog.csdn.net/qq_21794823/article/details/53068351
https://blog.csdn.net/daiyudong2020/article/details/51946080

源码：

#include #include #include #include #include #include #include #include #include #define pri(fmt, ...)printf("["__FILE__"][%s]-%d: " ,__FUNCTION__,__LINE__ ); \ printf(fmt, ##__VA_ARGS__); extern int h_errno; int main(int argc, char *argv[]) { if(2 != argc) { printf("Param Num Error ! \n"); return -1; } char *name = argv[1]; struct hostent *host = gethostbyname(name); int i; if(NULL == host) { pri("gethostbyname h_errno : %d \n", h_errno); return 0; } pri("host->h_name \t\t:%s \n", host->h_name); for(i=0; host->h_aliases[i]; i++) { pri("host->h_aliases[%d] \t\t:%s \n", i,(host->h_aliases[i])); } pri("host->h_addrtype \t\t:%s\n", (host->h_addrtype==AF_INET) ? "AF_INET": "AF_INET6"); pri("host->h_length \t\t:%d \n", host->h_length); for(i=0; host->h_addr_list[i]; i++) { pri("host->h_addr_list[%d] \t:%s \n", i,inet_ntoa(*(struct in_addr*)(host->h_addr_list[i]))); } return 0; }

编译运行测试：

root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname# gcc -o test test.c root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname# ./testwww.baidu.com [test.c][main]-34: host->h_name:www.a.shifen.com [test.c][main]-37: host->h_aliases[0]:www.baidu.com [test.c][main]-39: host->h_addrtype:AF_INET [test.c][main]-40: host->h_length:4 [test.c][main]-44: host->h_addr_list[0]:14.215.177.39 [test.c][main]-44: host->h_addr_list[1]:14.215.177.38 root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname# ./testwww.qq.com [test.c][main]-34: host->h_name:public.sparta.mig.tencent-cloud.net [test.c][main]-37: host->h_aliases[0]:www.qq.com [test.c][main]-39: host->h_addrtype:AF_INET [test.c][main]-40: host->h_length:4 [test.c][main]-44: host->h_addr_list[0]:14.18.175.154 [test.c][main]-44: host->h_addr_list[1]:113.96.232.215 root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname# ./testwww.alibaba.com [test.c][main]-34: host->h_name:hz-scproxy.alibaba.com.gds.alibabadns.com [test.c][main]-37: host->h_aliases[0]:www.alibaba.com [test.c][main]-37: host->h_aliases[1]:www.alibaba.com.gds.alibabadns.com [test.c][main]-37: host->h_aliases[2]:hz-scproxy.alibaba.com [test.c][main]-39: host->h_addrtype:AF_INET [test.c][main]-40: host->h_length:4 [test.c][main]-44: host->h_addr_list[0]:106.11.208.151 root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname#

gethostbyname 函数介绍（可以使用 man gethostbyname获取下述内容）：
头文件：

#include

函数原型：

struct hostent *gethostbyname(const char *name);

函数描述：

The gethostbyname() function returns a structure of type hostent for the given host name.Here name is either a hostname, or an IPv4 address in standard dot notation(asfor inet_addr(3)), or an IPv6 address in colon (and possibly dot) notation.(See RFC 1884 for the description of IPv6 addresses.)If name is an IPv4 or IPv6 address, no lookup is performed and gethostbyname() simply copies name into the h_name field and its struct in_addr equivalent into the h_addr_list[0] field of the returnedhostentstructure.If namedoesn'tendina dot and the environment variable HOSTALIASES is set, the alias file pointed to by HOSTALIASES will first be searched for name (see hostname(7) for the file format).The current domain and its parents are searched unless name ends in a dot.

我理解的大致意思是 :

函数根据输入的name 返回一个结构体 hostent。
输入的name可以是主机域名，也可以点分十进制格式（IPV4/IPV6）。
如果输入的是IPV4/IPV6格式，那么在gethostbyname函数中，只是简单的把 name 复制给 h_name(hostent 结构体中的元素)。
。。。

测试如下：

root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname# ./test106.11.208.151 [test.c][main]-34: host->h_name:106.11.208.151 [test.c][main]-39: host->h_addrtype:AF_INET [test.c][main]-40: host->h_length:4 [test.c][main]-44: host->h_addr_list[0]:106.11.208.151 root@ubuntu:/home/samba/03_test/02_Linux/gethostbyname#

hostent 结构体：

The hostent structure is defined in as follows:struct hostent { char*h_name; /* official name of host */ char **h_aliases; /* alias list */ inth_addrtype; /* host address type */ inth_length; /* length of address */ char **h_addr_list; /* list of addresses */ } #define h_addr h_addr_list[0] /* for backward compatibility */The members of the hostent structure are:h_name The official name of the host.h_aliases An array of alternative names for the host, terminated by a NULL pointer.h_addrtype The type of address; always AF_INET or AF_INET6 at present.h_length The length of the address in bytes.h_addr_list An array of pointers to network addresses for the host (in network byte order), terminated by a NULL pointer.h_addr The first address in h_addr_list for backward compatibility.

返回值

RETURN VALUE The gethostbyname() and gethostbyaddr() functions return the hostent structure or a NULL pointer if an error occurs.On error, the h_errnovariableholdsanerrornumber. When non-NULL, the return value may point at static data, see the notes below.

【Linux:通过域名，获取IP地址函数使用】失败，返回NULL，错误值保存在h_errno中。