How to define variables in php

1. Define constants

define("CONSTANT", "Hello world.")；

Constants can only contain scalar data (boolean, integer, float and string). When calling constants, only You need to simply use the name to get the value of the constant without adding the "$" sign.

Note: Constants and (global) variables are in different namespaces. This means for example TRUE and $TRUE are different.

2. Ordinary variables

$a = "hello";

3. Variable variables

$$a = "world";

Both variables are defined, $ The content of a is "hello" and the content of $hello is "world".

4. Static variables

Inside the function:

static $a = 0;

Note: uses the result of the expression in the declaration to Assignment will cause parsing errors

Static variables only exist in the local function domain (inside the function). After the function is executed, the variable value will not be lost and can be used for recursive calls.

5. Global variables

Global variables defined within the function body can be used outside the function body. Global variables defined outside the function body cannot be used within the function body. Global variables can be used outside the function body. To access variables within the scope, you can use special PHP to customize the $GLOBALS array:

$GLOBALS["b"] = $GLOBALS["a"] + $GLOBALS["b"];

A real global variable imported with the global statement in a function domain actually establishes a reference to the global variable

Note: The static and global definitions of variables are implemented in an application manner.

6. Assign a value to a variable

Assignment by address (simple reference)

$bar = &$foo; //加&符号到将要赋值的变量前

Changing the new variable will affect the original variable. This kind of assignment Operation is faster.

Note: Only named variables can be passed for address assignment

Recommended tutorial: PHP video tutorial

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