PHP致命错误：常量表达式包含无效操作 [英] PHP Fatal error: Constant expression contains invalid operations

问题描述

这是致命错误：

致命错误：常量表达式包含无效运算

Fatal error: Constant expression contains invalid operations

此代码中出现致命错误：

I get a fatal error in this code:

<?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php 7 。为什么显示此错误？谢谢

i am using php 7. why is this error showing? thanks

推荐答案

请改为这样做

<?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";

    ...
}

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