PHP5 + introduces the concept of $ GLOBALS delayed initialization _ PHP Tutorial

PHP5 + introduces the $ GLOBALS delay initialization concept. To use $ GLOBALS [_ SERVER] instead of $ _ SERVER to access related environment variables, the _ SERVERundefined error is always reported. Use Case 1 :? Phpprint_r ($ GLOBALS) today I want to use $ GLOBALS ['_ server'] to replace $ _ SERVER to access related environment variables. the error "_ SERVER undefined" is always reported. Use cases:

Case 1:

Print_r ($ GLOBALS );

At this time, the output does not contain _ SERVER information:

Array

(

[GLOBALS] => Array

* RECURSION *

[_ POST] => Array

(

)

[_ GET] => Array

(

)

[_ COOKIE] => Array

(

)

[_ FILES] => Array

(

)

)

Case 2:

Print_r ($ GLOBALS );

Print_r ($ _ SERVER );

The output contains _ SERVER information:

Array

(

[GLOBALS] => Array

* RECURSION *

[_ POST] => Array

(

)

[_ GET] => Array

(

)

[_ COOKIE] => Array

(

)

[_ FILES] => Array

(

)

[_ SERVER] => Array

(

)

)

Check the description of $ GLOBALS in the PHP manual and reference the comments of therandshow at gmail dot com:

Therandshow at gmail dot com

As of PHP 5.4 $ GLOBALS is now initialized just-in-time. This means there now is an advantage to not use

The $ GLOBALS variable as you can avoid the overhead of initializing it. How much of an advantage that is

I'm not sure, but I 've ve never liked $ GLOBALS much anyways.

Trace the root data source and find the PHP5Changelog update log description:

Unordered List ItemImproved Zend Engine, performance tweaks and optimizations

Unordered List ItemChanged $ GLOBALS into a JIT autoglobal, so it's initialized only if used. (this may affect opcode caches !) Www.2cto.com

718; When enabled, the SERVER and ENV variables are created when they're first

719; used (Just In Time) instead of when the script starts. If these variables

720; are not used within a script, having this directive on will result in

721; performance gain. The PHP directives register_globals, register_long_arrays,

722; and register_argc_argv must be disabled for this directive to have any affect.

723; http://php.net/auto-globals-jit

724 auto_globals_jit = On

Finally, we can understand that when auto_globals_jit = On is enabled in PHP5 +, the $ _ SERVER variable and the $ _ ENV variable will not be created when the script is started, instead, it is created when $ SERVER and $ ENV are used for the first time. Therefore, the above two cases may occur.

Note:

Conclusion:

Auto_globals_jit setting is also affecting $ _ REQUEST superglobal in 5.3 It is not explicitly stated in documentation.

When auto_globals_jit = On is enabled at least in version 5.3.13, $ _ REQUEST is created only when it is used for the first time.

Undefined error. Use Case 1 :? Php print_r ($ GLOBALS )...