Difference between global and $ globals [''] in PHP

Many people think that the difference between global and $ globals [] is actually not the same.

According to the official explanation

1. $ globals ['var'] is an external global variable.

2. Global $ VaR is an external reference or pointer with the same name as $ var.

For example:

1. <? PHP
2. $ Var1 = 1;
3. $ Var2 = 2;
4. Function Test (){
5. $ Globals ['var2'] = & $ globals ['var1'];
6. }
7. Test ();
8. Echo $ var2;
9. ?>

<? PHP $ var1 = 1; $ var2 = 2; function test () {$ globals ['var2'] = & $ globals ['var1'];} test (); echo $ var2;?>

The normal print result is 1.

1. <? PHP
2. $ Var1 = 1;
3. $ Var2 = 2;
4. Function Test (){
5. Global $ var1, $ var2;
6. $ Var2 = & $ var1;
7. }
8. Test ();
9. Echo $ var2;
10. ?>

<? PHP $ var1 = 1; $ var2 = 2; function test () {Global $ var1, $ var2; $ var2 = & $ var1;} test (); echo $ var2;?>

The unexpected result is 2.

Why is the result 2 printed? In fact, it is because the $ var1 reference points to the reference address of $ var2. The actual value is not changed.

Let's look at an example.

1. <? PHP
2. $ Var1 = 1;
3. Function Test (){
4. Unset ($ globals ['var1']);
5. }
6. Test ();
7. Echo $ var1;
8. ?>

<? PHP $ var1 = 1; function test () {unset ($ globals ['var1']);} test (); echo $ var1;?>

Because $ var1 is deleted, nothing is printed.

1. <? PHP
2. $ Var1 = 1;
3. Function Test (){
4. Global $ var1;
5. Unset ($ var1 );
6. }
7. Test ();
8. Echo $ var1;
9. ?>

<? PHP $ var1 = 1; function test () {Global $ var1; unset ($ var1) ;}test (); echo $ var1 ;?>

Accidentally printed 1. It indicates that only the alias is deleted. | the referenced value is not changed.

Do you understand?

That is to say, global $ VaR is actually $ Var = & $ globals ['var']. Call an alias of an external variable.