PHP Fatal error: Constant expression contains invalid operations

Question

here is the fatal error:

Fatal error: Constant expression contains invalid operations

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"; ... }

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

Because $_SERVER['HTTP_USER_AGENT']; is "run-time" information; and class property declaration may include an initialization, but this initialization must be a constant value -- that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated. — Mark Baker
– Mark Baker, Commented Jan 2, 2017 at 0:13
You assign it in the class constructor, and instatiate an object... and wtf is global $user_agent; supposed to be? Is it something that should be passed as an argument to the method? — Mark Baker
– Mark Baker, Commented Jan 2, 2017 at 0:15
@MarkBaker i dont know, i got this from this post: stackoverflow.com/a/18070424/4357238 — pixie123
– pixie123, Commented Jan 2, 2017 at 0:17
The problem is that constant does not have a value when that line is executed by PHP. To resolve it, you can initialise the variable as an empty string, and then assign it a value inside the method. However, this code is bad design. Perhaps you should try to restructure the flow. — Amal
– Amal, Commented Jan 2, 2017 at 0:28

funsholaniyi · Accepted Answer · 2017-01-02 01:08:08Z

Do This Instead

<?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"; ... }

Hope it Helps

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