下面是更安全版本的接受答案的基础，使用PHP的filter_input函数，这也弥补了$_SERVER['REQUEST_URI']的潜在缺失:

$protocol_https = filter_input(INPUT_SERVER, 'HTTPS', FILTER_SANITIZE_STRING);
$host = filter_input(INPUT_SERVER, 'HTTP_HOST', FILTER_SANITIZE_URL);
$request_uri = filter_input(INPUT_SERVER, 'REQUEST_URI', FILTER_SANITIZE_URL);
if(strlen($request_uri) == 0)
{
    $request_uri = filter_input(INPUT_SERVER, 'SCRIPT_NAME', FILTER_SANITIZE_URL);
    $query_string = filter_input(INPUT_SERVER, 'QUERY_STRING', FILTER_SANITIZE_URL);
    if($query_string)
    {
        $request_uri .= '?' . $query_string;
    }
}
$full_url = ($protocol_https ? 'https' : 'http') . '://' . $host . $request_uri;

你可以使用一些不同的过滤器来调整它到你的喜欢。

在网页上输出链接的简短版本

$url =  "//{$_SERVER['HTTP_HOST']}{$_SERVER['REQUEST_URI']}";

$escaped_url = htmlspecialchars( $url, ENT_QUOTES, 'UTF-8' );
echo '<a href="' . $escaped_url . '">' . $escaped_url . '</a>';

下面是关于//example.com/path/格式的问题和边缘情况的更多细节

完整版

function url_origin( $s, $use_forwarded_host = false )
{
    $ssl      = ( ! empty( $s['HTTPS'] ) && $s['HTTPS'] == 'on' );
    $sp       = strtolower( $s['SERVER_PROTOCOL'] );
    $protocol = substr( $sp, 0, strpos( $sp, '/' ) ) . ( ( $ssl ) ? 's' : '' );
    $port     = $s['SERVER_PORT'];
    $port     = ( ( ! $ssl && $port=='80' ) || ( $ssl && $port=='443' ) ) ? '' : ':'.$port;
    $host     = ( $use_forwarded_host && isset( $s['HTTP_X_FORWARDED_HOST'] ) ) ? $s['HTTP_X_FORWARDED_HOST'] : ( isset( $s['HTTP_HOST'] ) ? $s['HTTP_HOST'] : null );
    $host     = isset( $host ) ? $host : $s['SERVER_NAME'] . $port;
    return $protocol . '://' . $host;
}

function full_url( $s, $use_forwarded_host = false )
{
    return url_origin( $s, $use_forwarded_host ) . $s['REQUEST_URI'];
}

$absolute_url = full_url( $_SERVER );
echo $absolute_url;

这是一个经过大量修改的http://snipplr.com/view.php?codeview&id=2734(现在已经不存在了)

URL结构:

scheme：//username：password@domain：port/path？query_string#fragment_id

粗体部分将不包含在函数中

注:

This function does not include username:password from a full URL or the fragment (hash). It will not show the default port 80 for HTTP and port 443 for HTTPS. Only tested with http and https schemes. The #fragment_id is not sent to the server by the client (browser) and will not be added to the full URL. $_GET will only contain foo=bar2 for an URL like /example?foo=bar1&foo=bar2. Some CMS's and environments will rewrite $_SERVER['REQUEST_URI'] and return /example?foo=bar2 for an URL like /example?foo=bar1&foo=bar2, use $_SERVER['QUERY_STRING'] in this case. Keep in mind that an URI = URL + URN, but due to popular use, URL now means both URI and URL. You should remove HTTP_X_FORWARDED_HOST if you do not plan to use proxies or balancers. The spec says that the Host header must contain the port number unless it is the default number.

客户端(浏览器)控制变量:

$ _SERVER [' REQUEST_URI ']。任何不支持的字符在发送之前都由浏览器编码。 $_SERVER['HTTP_HOST']，根据PHP手册中的注释:http://php.net/manual/en/reserved.variables.php并不总是可用的 $_SERVER['HTTP_X_FORWARDED_HOST']由平衡器设置，在PHP手册中的$_SERVER变量列表中没有提到。

服务器控制变量:

$ _SERVER(“HTTPS”)。客户端选择使用此选项，但服务器返回的实际值为空或“on”。 $ _SERVER [' SERVER_PORT ']。服务器只接受允许的数字作为端口。 $ _SERVER [' SERVER_PROTOCOL ']。服务器只接受特定的协议。 $ _SERVER [' SERVER_NAME ']。它是在服务器配置中手动设置的，根据kralyk的说法，它不适用于IPv6。

相关:

PHP中的HTTP_HOST和SERVER_NAME之间的区别是什么? HTTP“主机”头参数中需要端口号吗? https://stackoverflow.com/a/28049503/175071

非常简单的用法:

function current_url() {
    $current_url  = ( $_SERVER["HTTPS"] != 'on' ) ? 'http://'.$_SERVER["SERVER_NAME"] :  'https://'.$_SERVER["SERVER_NAME"];
    $current_url .= ( $_SERVER["SERVER_PORT"] != 80 ) ? ":".$_SERVER["SERVER_PORT"] : "";
    $current_url .= $_SERVER["REQUEST_URI"];

    return $current_url;
}

使用Apache环境变量很容易做到这一点。这只适用于Apache 2，我假设您正在使用Apache 2。

简单使用下面的PHP代码:

<?php
    $request_url = apache_getenv("HTTP_HOST") . apache_getenv("REQUEST_URI");
    echo $request_url;
?>

我觉得这个方法不错，试试吧

if($_SERVER['HTTP_HOST'] == "localhost"){
    define('SITEURL', 'http://' . $_SERVER['HTTP_HOST']);
    define('SITEPATH', $_SERVER['DOCUMENT_ROOT']);
    define('CSS', $_SERVER['DOCUMENT_ROOT'] . '/css/');
    define('IMAGES', $_SERVER['DOCUMENT_ROOT'] . '/images/');
}
else{
    define('SITEURL', 'http://' . $_SERVER['HTTP_HOST']);
    define('SITEPATH', $_SERVER['DOCUMENT_ROOT']);
    define('TEMPLATE', $_SERVER['DOCUMENT_ROOT'] . '/incs/template/');
    define('CSS', $_SERVER['DOCUMENT_ROOT'] . '/css/');
    define('IMAGES', $_SERVER['DOCUMENT_ROOT'] . '/images/');
}

简单的使用方法:

$uri = $_SERVER['REQUEST_SCHEME'] . '://' . $_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI']