How to use external variables in methods in php

Method: 1. Use the global keyword and use the "global $external variable name;" statement within the method to import external variables; 2. Use the "$GLOBALS" variable and directly use "$ GLOBALS['a']" statement can refer to external variables; 3. Use value transfer to pass external variables in as parameters.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

Today I wrote a program using pure native PHP Method, when you want to call external global variables, the result: either an error is reported, or there is no output?

Let’s talk about the reasons and solutions:

Variable scope

In user-defined methods (functions), a Local function scope will be introduced. Any variables used inside a function will be restricted to the local function scope by default. For example:

<?php
$a = 1; /* global scope */

function Test()
{
    echo $a; /* reference to local scope variable */
}

Test();
?>

This script will not produce any output because the echo statement refers to a local version of the variable $a, and it is not assigned a value in this scope.

You may notice that PHP's global variables are a little different from C language. In C language, global variables automatically take effect in functions unless overridden by local variables. This may cause some problems, someone may accidentally change a global variable. Global variables in PHP must be declared global when used in functions.

The first solution: global keyword---declare variables outside the function globally within the function

<?php
$a = 1;
$b = 2;
$c = 3;
function demo(){
	global $a,$b,$c;
    echo &#39;$a = &#39;.$a;
    echo &#39;<br>$b = &#39;.$b;
    echo &#39;<br>$c = &#39;.$c;
}
demo();
?>

Look at the output result:

Analysis: The function of

global keyword is: import global variables, use global variable 1, variable 2, ... In the form of importing global variable 1, variable 2... into the local scope of a function, the global variables defined outside the function can be used inside the function.

You need to pay attention to the following points when using the global keyword:

• The global keyword can only be used inside the function, not outside the function;

• The global keyword can only be used to refer to global variables outside the function, and cannot be directly assigned when referencing. The assignment and declaration statements need to be written separately;

• In the function When a variable modified with the global keyword is destroyed internally, variables outside the function are not affected.

The second solution: use the $GLOBALS super global variable

<?php
$a = 1;
$b = 2;
$c = 3;
function demo(){
    echo &#39;$a = &#39;.$GLOBALS[&#39;a&#39;];
    echo &#39;<br>$b = &#39;.$GLOBALS[&#39;b&#39;];
    echo &#39;<br>$c = &#39;.$GLOBALS[&#39;c&#39;];
}
demo();
?>

The output result is:

Analysis:

$GLOBALS is a predefined variable (also called a super global variable), which is a global combination array containing all variables. The name of the variable is the array. Key, you can use the form $GLOBALS['variable name'] to access the specified global variable. As long as it is a global variable that has appeared, it can be obtained through the $GLOBALS array.

The difference between global and $GLOBALS

• global can only be used inside the function, not outside the function; while $GLOBALS can be used in the program It can be used anywhere (inside and outside functions).

• When a variable modified with the global keyword is destroyed inside a function, variables outside the function are not affected; $GLOBALS is.

  Reason:

  When using the global keyword to modify the $var variable, it is a reference to the variable of the same name outside the function, and the inside and outside are two variables that do not affect each other;

  And $GLOBALS['var'] refers to the external variable of the function itself, which is a variable.

The third solution: pass the external variables of the function into parameters

<?php  
header(&#39;content-type:text/html;charset=utf-8&#39;);   
$mytext="PHP中文网";

function chao_echo($mytext){
    echo $mytext;
}

chao_echo($mytext);
?>

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