PHP致命错误：常量表达式包含无效操作

Question

这是致命错误：

致命错误：常量表达式包含无效操作

我在此代码中遇到致命错误：

<?php

class InfoClass {

    private $user_agent = $_SERVER['HTTP_USER_AGENT']; // error is on this line

    public static function getOS() { 

        global $user_agent;

        $os_platform = "Unknown OS Platform";

        ...
}

我正在使用PHP7。为什么显示此错误？谢谢

Answer 1

改为这样做

<?php

class InfoClass {
    private $user_agent;
    public function __construct(){
        $this->user_agent = $_SERVER['HTTP_USER_AGENT']; // error is on this line
    }

    public static function getOS() { 

    global $user_agent;

    $os_platform = "Unknown OS Platform";

    ...
}

希望能帮助到你