PHP获取主机名、域名函数

今天看到几个函数，可以根据ip地址  /  域名 获取对应的 域名 / ip 的函数。记录于此。

gethostbynamel($hostname) // 根据域名获取IP，返回一个数组，比如baidu。com，就返回2个ip

说明
array gethostbynamel ( string $hostname )
Returns a list of IPv4 addresses to which the Internet host specified by hostname resolves. 

参数
hostname The host name. 

返回值
Returns an array of IPv4 addresses or FALSE if hostname could not be resolved. 

 gethostbyname($hostname)  // 根据域名获取IP，只返回第一个IP

gethostbyname — Get the IPv4 address corresponding to a given Internet host name 

说明
string gethostbyname ( string $hostname )
Returns the IPv4 address of the Internet host specified by hostname. 

参数
hostname The host name. 

返回值
Returns the IPv4 address or a string containing the unmodified hostname on failure. 

 gethostbyaddr($ip)  // 根据IP 获取域名

gethostbyaddr — Get the Internet host name corresponding to a given IP address 

说明
string gethostbyaddr ( string $ip_address )
Returns the host name of the Internet host specified by ip_address. 

参数
ip_address 
The host IP address. 

返回值
Returns the host name on success, the unmodified ip_address on failure, or FALSE on malformed input. 

 例子：

$hostname = 'www.baidu.com';
$addr = '127.0.0.1';

print_r(gethostbyname($hostname));
echo '<br>';

print_r(gethostbyaddr($addr));
echo '<br>';

print_r(gethostbynamel($hostname));

输出

220.181.111.148
idc-wang
Array ( [0] => 220.181.111.148 [1] => 220.181.112.143 )