PHP通过访问第三方接口，根据IP地址获取所在城市

<?php
header('Content-Type:text/html;Charset=utf-8');

/**
 * 获取IP地址
 *
 * @return string
 */
function get_ip() {
	$realip = '';
	$unknown = 'unknown';
	if (isset($_SERVER)) {
		if (isset($_SERVER['HTTP_X_FORWARDED_FOR']) && !empty($_SERVER['HTTP_X_FORWARDED_FOR']) && strcasecmp($_SERVER['HTTP_X_FORWARDED_FOR'], $unknown)) {
			$arr = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
			foreach ($arr as $ip) {
				$ip = trim($ip);
				if ($ip != 'unknown') {
					$realip = $ip;
					break;
				}
			}
		} else if (isset($_SERVER['HTTP_CLIENT_IP']) && !empty($_SERVER['HTTP_CLIENT_IP']) && strcasecmp($_SERVER['HTTP_CLIENT_IP'], $unknown)) {
			$realip = $_SERVER['HTTP_CLIENT_IP'];
		} else if (isset($_SERVER['REMOTE_ADDR']) && !empty($_SERVER['REMOTE_ADDR']) && strcasecmp($_SERVER['REMOTE_ADDR'], $unknown)) {
			$realip = $_SERVER['REMOTE_ADDR'];
		} else {
			$realip = $unknown;
		}
	} else {
		if (getenv('HTTP_X_FORWARDED_FOR') && strcasecmp(getenv('HTTP_X_FORWARDED_FOR'), $unknown)) {
			$realip = getenv("HTTP_X_FORWARDED_FOR");
		} else if (getenv('HTTP_CLIENT_IP') && strcasecmp(getenv('HTTP_CLIENT_IP'), $unknown)) {
			$realip = getenv("HTTP_CLIENT_IP");
		} else if (getenv('REMOTE_ADDR') && strcasecmp(getenv('REMOTE_ADDR'), $unknown)) {
			$realip = getenv("REMOTE_ADDR");
		} else {
			$realip = $unknown;
		}
	}
	$realip = preg_match("/[\d\.]{7,15}/", $realip, $matches) ? $matches[0] : $unknown;
	return $realip;
}

/**
 * 根据IP获取地址详情
 *
 * @param string $ip
 * @return bool|mixed
 */
function get_ip_info($ip = '') {
	if (empty($ip)) {
		$ip = get_ip();
	}

	$res = @file_get_contents('http://int.dpool.sina.com.cn/iplookup/iplookup.php?format=js&ip=' . $ip);
	if (empty($res)) {
		return false;
	}

	$jsonMatches = array();
	preg_match('#\{.+?\}#', $res, $jsonMatches);
	if (!isset($jsonMatches[0])) {
		return false;
	}

	$json = json_decode($jsonMatches[0], true);
	if (isset($json['ret']) && $json['ret'] == 1) {
		$json['ip'] = $ip;
		unset($json['ret']);
	} else {
		return false;
	}

	return $json;
}

$ipInfos = get_ip_info('123.125.114.144'); // baidu.com IP地址
print_r($ipInfos);

输出：

【特别说明】

使用 file_get_contents() 函数一定要加个超时时间设置，否则，网络差的时候会拖垮php-fpm进程！

参考：

http://blog.csdn.net/liruxing1715/article/details/28238483