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 a constant, you only need to simply use the name to get the value of the constant, without adding the "$" symbol, such as: echo CONSTANT;

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

2. Ordinary variables

$a = "hello";

3. Variable variables (use two dollar signs ($))

$$a = "world";

Both variables are defined. The content of $a is "hello" and the content of $hello is "world". Therefore, it can be expressed as:

echo "$a ${$a}";

or

echo "$a $hello";

They will both output: hello world.

4. Static variables

static $a = 0 inside the function;

Note: Use expressions in declarations Assigning the result to it will cause parsing errors such as static $a =3 3; (error).

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

For example:

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

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

global $obj;

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 assignment operation is faster.

Note: Only named variables can be assigned addresses. If

$bar = &$a;
$bar = &$foo;

changes the value of $bar, it can only change the value of variable foo, but not the value of variable foo. The value of a (the reference changed).

Recommended tutorial: PHP video tutorial

The above is the detailed content of How to define variables in php. For more information, please follow other related articles on the PHP Chinese website!