PHP致命误差:常数表达式包含无效的操作

Question

这是致命错误：

致命错误：常数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

而不是这样做

<?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";
    ...
}

希望它有帮助