快速解决方案(无错误)

function getClientIP():string
{
    $keys=array('HTTP_CLIENT_IP','HTTP_X_FORWARDED_FOR','HTTP_X_FORWARDED','HTTP_FORWARDED_FOR','HTTP_FORWARDED','REMOTE_ADDR');
    foreach($keys as $k)
    {
        if (!empty($_SERVER[$k]) && filter_var($_SERVER[$k], FILTER_VALIDATE_IP))
        {
            return $_SERVER[$k];
        }
    }
    return "UNKNOWN";
}

<?php
/**
 * Function to get the client ip address
 *
 * @return string The Ip address
 */
function getIp(): string {
    if (! empty($_SERVER['HTTP_CLIENT_IP'])) {
        return $_SERVER['HTTP_CLIENT_IP'];
    }

    if (! empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        return $_SERVER['HTTP_X_FORWARDED_FOR'];
    }

    return $_SERVER['REMOTE_ADDR'] ?? '?';
}

更小的

/**
 * Function to get the client ip address
 *
 * @return string The Ip address
 */
function getIp(): string {
    return $_SERVER['HTTP_CLIENT_IP'] ?? $_SERVER['HTTP_X_FORWARDED_FOR'] ?? $_SERVER['REMOTE_ADDR'] ?? '';
}

下面的函数确定所有的可能性，并以逗号分隔的格式返回值(ip, ip等)。

它还有一个可选的验证功能(默认禁用的第一个参数)，用于根据(私有范围和保留范围)验证IP地址。

<?php
echo GetClientIP(true);

function GetClientIP($validate = False) {
  $ipkeys = array(
  'REMOTE_ADDR',
  'HTTP_CLIENT_IP',
  'HTTP_X_FORWARDED_FOR',
  'HTTP_X_FORWARDED',
  'HTTP_FORWARDED_FOR',
  'HTTP_FORWARDED',
  'HTTP_X_CLUSTER_CLIENT_IP'
  );

  /*
  Now we check each key against $_SERVER if containing such value
  */
  $ip = array();
  foreach ($ipkeys as $keyword) {
    if (isset($_SERVER[$keyword])) {
      if ($validate) {
        if (ValidatePublicIP($_SERVER[$keyword])) {
          $ip[] = $_SERVER[$keyword];
        }
      }
      else{
        $ip[] = $_SERVER[$keyword];
      }
    }
  }

  $ip = ( empty($ip) ? 'Unknown' : implode(", ", $ip) );
  return $ip;
}

function ValidatePublicIP($ip){
  if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE)) {
    return true;
  }
  else {
    return false;
  }
}

下面是一个很好的获取用户IP地址的干净代码示例。

$ip = $_SERVER['HTTP_CLIENT_IP'] 
   ? $_SERVER['HTTP_CLIENT_IP'] 
   : ($_SERVER['HTTP_X_FORWARDED_FOR'] 
        ? $_SERVER['HTTP_X_FORWARDED_FOR'] 
        : $_SERVER['REMOTE_ADDR']);

下面是一个使用elvis操作符的简短版本:

$_SERVER['HTTP_CLIENT_IP'] 
   ? : ($_SERVER['HTTP_X_FORWARDED_FOR'] 
   ? : $_SERVER['REMOTE_ADDR']);

下面是一个使用isset删除通知的版本(谢谢你，@shasi kanth):

$ip = isset($_SERVER['HTTP_CLIENT_IP']) 
    ? $_SERVER['HTTP_CLIENT_IP'] 
    : (isset($_SERVER['HTTP_X_FORWARDED_FOR']) 
      ? $_SERVER['HTTP_X_FORWARDED_FOR'] 
      : $_SERVER['REMOTE_ADDR']);

echo $_SERVER['REMOTE_ADDR'];

http://php.net/manual/en/reserved.variables.server.php

以下是我发现的最先进的方法，我在过去已经尝试过其他一些方法。确保获得访问者的IP地址是有效的(但请注意，任何黑客都很容易伪造IP地址)。

function get_ip_address() {

    // Check for shared Internet/ISP IP
    if (!empty($_SERVER['HTTP_CLIENT_IP']) && validate_ip($_SERVER['HTTP_CLIENT_IP'])) {
        return $_SERVER['HTTP_CLIENT_IP'];
    }

    // Check for IP addresses passing through proxies
    if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {

        // Check if multiple IP addresses exist in var
        if (strpos($_SERVER['HTTP_X_FORWARDED_FOR'], ',') !== false) {
            $iplist = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
            foreach ($iplist as $ip) {
                if (validate_ip($ip))
                    return $ip;
            }
        }
        else {
            if (validate_ip($_SERVER['HTTP_X_FORWARDED_FOR']))
                return $_SERVER['HTTP_X_FORWARDED_FOR'];
        }
    }
    if (!empty($_SERVER['HTTP_X_FORWARDED']) && validate_ip($_SERVER['HTTP_X_FORWARDED']))
        return $_SERVER['HTTP_X_FORWARDED'];
    if (!empty($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']) && validate_ip($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']))
        return $_SERVER['HTTP_X_CLUSTER_CLIENT_IP'];
    if (!empty($_SERVER['HTTP_FORWARDED_FOR']) && validate_ip($_SERVER['HTTP_FORWARDED_FOR']))
        return $_SERVER['HTTP_FORWARDED_FOR'];
    if (!empty($_SERVER['HTTP_FORWARDED']) && validate_ip($_SERVER['HTTP_FORWARDED']))
        return $_SERVER['HTTP_FORWARDED'];

    // Return unreliable IP address since all else failed
    return $_SERVER['REMOTE_ADDR'];
}

/**
 * Ensures an IP address is both a valid IP address and does not fall within
 * a private network range.
 */
function validate_ip($ip) {

    if (strtolower($ip) === 'unknown')
        return false;

    // Generate IPv4 network address
    $ip = ip2long($ip);

    // If the IP address is set and not equivalent to 255.255.255.255
    if ($ip !== false && $ip !== -1) {
        // Make sure to get unsigned long representation of IP address
        // due to discrepancies between 32 and 64 bit OSes and
        // signed numbers (ints default to signed in PHP)
        $ip = sprintf('%u', $ip);

        // Do private network range checking
        if ($ip >= 0 && $ip <= 50331647)
            return false;
        if ($ip >= 167772160 && $ip <= 184549375)
            return false;
        if ($ip >= 2130706432 && $ip <= 2147483647)
            return false;
        if ($ip >= 2851995648 && $ip <= 2852061183)
            return false;
        if ($ip >= 2886729728 && $ip <= 2887778303)
            return false;
        if ($ip >= 3221225984 && $ip <= 3221226239)
            return false;
        if ($ip >= 3232235520 && $ip <= 3232301055)
            return false;
        if ($ip >= 4294967040)
            return false;
    }
    return true;
}