Analysis of classic application and precautions for PHP global global variables [Comparison of usage with $GLOBALS] Original

This article describes the use and precautions of PHP global global variables. Share it for your reference, as follows:

Use global to declare the external variable as a global variable in the method, that is, the variable can be called.

Example 1. Basic usage of global

<?php
$a=1;
$b=2;
test_global();
function test_global() {
  global $a,$b;
  echo $a+$b; //Output 3}

Example 2. Global Reference

<?php
$var $a=1;
function test(){
  global $a;
  $a++;
  unset($a);
}
test();
echo $a;

Running results:

2

Notice:

1. The global in the function here refers to the external $a, which is a reference or pointer of the same name as the external variable $a. Therefore, $a++ inside the function can change the value of the external $a.

2. unset($a) is a deleted alias reference and has no effect on the value of the variable.

Supplement: $GLOBALS['var'] global variable application

<?php
$a = 1;
function test(){
  unset($GLOBALS['a']);
}
test();
echo $a;

Run the above code and the output is empty!

Notice:Here $GLOBALS['a'] is the external variable itself! That is: global $a is equivalent to &$GLOBALS['a'].

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