Analysis of global and $globals[in the PHP language
PHP in the global and $globals not only the wording is not the same, 2 of the difference is still very large, in practical applications need to pay attention to!
Let's look at the following example:
Reference
The result of the execution is:
0
5
How could this be? Shouldn't it be 2 5? How can there be 1 0 and a 5?
Well, we keep the above questions in-depth analysis of $globals and global principles!
We all know that variables are actually "code names" in the code of the corresponding physical existence.
$globals Explanation of PHP Manual reference:
Reference
Global variables: $GLOBALS, note: $GLOBALS are available in PHP 3.0.0 and later versions.
An array that consists of all defined global variables. The variable name is the index of the array. This is a "superglobal", or can be described as an automatic global variable.
In other words, $var1 and $globals[' var1 ' in the above code refer to the same variable, not 2 different variables!
What does global do now?
explanation of the global reference to the PHP manual:
Reference
If a variable declared as global is assigned to a reference within a function, the reference is only visible inside the function. You can avoid this by using an array of $GLOBALS.
We all know that the variables generated by the functions in PHP are private variables of the function, then the variables generated by the Global keyword will certainly not escape the rule, why do you say, look at the following code:
Reference
The result of the execution is:
1
Why does it output 1? Didn't you give $ A to unset? Unset failed? PHP bug?
is not, in fact unset work, is the test function of $ A to unset dropped, you can add in the function test ()
Print $a;
To test!
Then go back to the above example 1, see Test_global in the Code "$var 2 =& $var 1;", above is a reference assignment operation, that is, $VAR2 will point to the physical memory address pointed to by var1, so example 1 after the Test_global function has been executed , the variable changes only in the function of the local effect, the function outside the $var2 point of the physical memory address does not change, or it itself.
At this point, you can understand why example 1 after execution, $var 2 is 0, and $VAR3 is 5!
So we come to the conclusion that the difference between global and $globals[in a function is:
GlobalWhen a function produces an alias variable that points to an external variable of the function, rather than the actual function external variable, but changes the pointing address of the alias variable, some unexpected situations occur, such as Example 1.
$GLOBALS []The actual call is an external variable, and the function remains consistent inside and outside
The following two columns can be compared to deepen the impression:
Global
Output: someting
$GLOBALS []:
Output: Empty
When you follow the above understanding, the following situation is not a bit dizzy?
The output will be "3″." The global variable $a and $b are declared in the function, and all reference variables of any variable are pointed to the global variable.
Why not 2, outside the function is not not affected, note that $b in the function is not modified by reference, but the modified $b point to the value of physical memory, so the external input is 3.
