1. Define the constant define("CONSTANT", "Hello world.");
Constants can only contain scalar data (boolean, integer, float, and string).
When calling a constant, you only need to simply obtain the value of the constant with the name, and you cannot add the "$" symbol, such as: echo CONSTANT;
Note: Constants and (global) variables are in different namespaces. This means that for example TRUE and $TRUE are different.
2. The normal variable $a = "hello";
3. Variable variables (using two dollar signs ($))
$$a = "world";
Both variables are defined:
The content of $a is "hello" and the content of $hello is "world".
Therefore, it can be expressed as:
echo "$a ${$a}"; or echo "$a $hello"; they all output: hello world
To use mutable variables for arrays, an ambiguous problem must be solved. This is when writing $$a[1], the parser needs to know whether he wants $a[1] as a variable, or wants $$a as a variable and take out the value indexed as [1] in that variable. The syntax to solve this problem is to use ${$a[1]} for the first case and ${$a}[1] for the second case.
4. Static variables
Inside the functionstatic $a = 0;
Note: Assigning values to the expression in the declaration will result in parsing errors such as static $a =3+3; (error)
Static variables only exist in the local function domain (inside the function). After the function is executed, the variable value will not be lost and can be used for recursive calls.
5. Global variables
Global variables defined in the function body can be used in the body of the function in vitro. Global variables defined in the function in vitro cannot be used in the body of the function. Accessing variables in a global scope can be customized with a special PHP.
like:$GLOBALS["b"] = $GLOBALS["a"] + $GLOBALS["b"];
A real global variable imported in a function domain using a global statement actually creates a reference to the global variable
global $obj;
Note: The static and global definitions of variables are implemented in the application way.
6. Assign value to variables: pass address assignment (simple reference):
$bar = &$foo; //Add the & symbol before the variable to be assigned
Changing new variables will affect the original variable, and this assignment operation is faster
Note: Only named variables can be assigned to address
Note: If
$bar = &$a;
$bar = &$foo;
Changing the value of $bar can only change the value of variable foo, but not the value of a (reference has changed)
Hyperglobal variable $GLOBALS:
Contains a variable that references a valid global scope to each current script. The key of this array is marked as the name of the global variable. The $GLOBALS array exists since PHP 3.
$_SERVER: The variable is set by the web server or is directly associated with the execution environment of the current script. Similar to the old array $HTTP_SERVER_VARS array (still valid, but not against use).
$_GET: A variable submitted to the script via the HTTP GET method.
$_POST: A variable submitted to the script via the HTTP POST method.
$_COOKIE: A variable submitted to the script via the HTTP Cookies method.
$_FILES: A variable submitted to the script via an HTTP POST file upload.
Enctype="multipart/form-data" must be included in the file upload form
$_ENV: The variable that executes the environment to the script.
$_REQUEST: A variable submitted to the script via the GET, POST, and COOKIE mechanisms, so the array is not trustworthy. All changes contained in this array
The existence of quantities and the order of variables are defined according to the variables_order configuration instructions in . This array does not directly simulate earlier versions of PHP 4.1.0. See import_request_variables().
Note: Since PHP 4.3.0, file information in $_FILES no longer exists in $_REQUEST.
$_SESSION: The variable currently registered to the script session.
How to disable phpinfo():
middle
disable_functions = phpinfo()
Restart the web server.
Constants in php
Constants can only use define (constant name, constant value);
Constants can only contain scalar data (boolean, integer, float, and string).
You can simply obtain the value of a constant by specifying its name, and do not prefix the constant with the $ symbol. If the constant name is dynamic, you can also use a function
constant() to read the value of a constant. Use get_defined_constants() to get a list of all defined constants.
Note: Constants and (global) variables are in different namespaces. This means that for example TRUE and $TRUE are different.
If an undefined constant is used, PHP assumes that the name of the constant itself is desired, as if it is called with a string (CONSTANT corresponds to "CONSTANT"). An E_NOTICE-level error will be issued. See why $w3sky[bar] is wrong in the manual (unless you define bar as a constant with define() in advance). If you just want to check whether a certain constant is defined, use the defined() function.
Constants and variables are different:
* The constant is not preceded by the dollar sign ($);
* Constants can only be defined using the define() function, and cannot be defined through assignment statements;
* Constants can be defined and accessed anywhere without paying attention to the rules of variable scope;
* Constants cannot be redefined or undefined once defined;
* The value of a constant can only be a scalar.
Define constants
<?PHP
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
?>
Summarize
The above is a summary of the various methods for defining variables in PHP introduced to you by the editor. I hope it will be helpful to you. If you have any questions, please leave me a message and the editor will reply to you in time. Thank you very much for your support for my website!