Global & never understood how it works

Global & amp; has never understood how it works $ var1 & nbsp ;=& nbsp; 1; $ var2 & nbsp ;=& nbsp; 2; function & nbsp; test () {global & nbsp; $ var1, $ var2; & nbsp; // & nbsp; $ var1 & nbsp ;=& nbsp; 3; /global & never understood how it works

$ Var1 = 1;
$ Var2 = 2;
Function test (){
Global $ var1, $ var2 ;//
$ Var1 = 3; // $ var1 re-assigned and no return
}
Test ();
Echo $ var1; // why is it 3

$ Var1 = 1;
$ Var2 = 2;
Function test (){
Global $ var1, $ var2;
$ Var1 = & var2;
}
Test ();
Echo $ var1 // 1 cannot be understood

$ Var1 = 1;
$ Var2 = 2;
Function test_global ()
{
Global $ var1, $ var2;
$ Var1 = & $ var2;
$ Var1 = 7;
}
Test_global ();
Echo $ var1;
Echo $ var2; // The result is 1 and 7

------ Solution --------------------
No parameters are passed in the three functions of the landlord.
The role of global is here.
When you do not need to pass the parameter in, you need to use this variable again. Global
------ Solution --------------------
Thank you. Next, let's talk about the role of "&" $ var1 = & var2. how can we understand it?
------ Solution --------------------
$ Var1 = 1;
$ Var2 = 2;
Function test (){
Global $ var1, $ var2;
$ Var1 = & var2;
}
Test ();
Echo $ var1 // 1 cannot be understood
The $ var1 = & var2; $ var1 in the test () function is only a local variable in the function and does not belong to a global variable. If $ var1 is printed in test (), the result $ var1 = 2 is displayed;
------ Solution --------------------
$ Var1 = 1;
$ Var2 = 2;
Function test_global ()
{
Global $ var1, $ var2;
$ Var1 = & $ var2;
$ Var1 = 7;
}
Test_global ();
Echo $ var1;
Echo $ var2; // The result is 1 and 7

Let's look at this. Similarly, $ var1 is still a local variable. However, in test (), $ var1 = & $ var2; the code points the value of $ var1 to the memory address corresponding to the pointer of $ var2 (as AA ). In this case, $ var1 = 7, that is, change AA to 7.
PHP reference, hope to help you understand.