PHP constants

 Php constants 

Constants are variables whose value cannot be changed during the script execution.

Two ways to define a constant:

1. Using the define () method.
2. Using the const keyword.
3.  constant() function

 

Note:- naming a constant, don't use $ symbol with the constant's name.

 

1.    Using define()

To create a constant.

Syntax:-

Define(name, value, case-insensitive)

Parameters:

1. Name: name of the constant
2. Value: value of the constant
3. Case-insensitive: specifies whether the constant name is case sensitive or not. It's default value is false, which means, by default, the constant name is case sensitive.

4.    <?Php 5.       6.    // this creates a case-sensitive constant 7.    Define("name", "ram"); 8.    Echo name, "\n"; 9.       10. // this creates a case-insensitive constant 11. Define("name1", "ram", true); 12. Echo name1; 13.    14. ?>

Output:

Ram

Ram

 

2.  Using the const keyword

Define constants in php using the const keyword.

Const keyword use for to define scalar constants, i.e. Only integers, floats, booleans and strings, not for array.

Define() can be used for  array.

Syntax

Constant(name)

<?Php   Const mesg="hello i am php constant ";   Echo mesg;   ?>

Output:

Hello i am php constant

 

Constants are global: by default, constants are automatically global, and can be used throughout the script, accessible inside and outside of any function.
Example:

<?Php    Define("abc", "hello constants");    Function xyz() {     echo abc; }     Xyz();    ?>

Hello constants

 

3.  Constant() function

For constants using constant() function instead of the echo statement.

Syntax

The syntax for the following constant function:

1.    Constant (name)  

 

<?Php      

    define("msg", "sjkpgm");  

    echo msg, "</br>";  

    echo constant("msg");  

    //both are similar  

?>  

Output:

Sjkpgm 

Sjkpgm

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 Php magic constants

Php provides a large number of predefined constants to any script which it runs.

There are five magical constants that change depending on where they are used.

These special constants are case-insensitive and are as follows −

Sr.no	Name & description	Syntax	Example
1	__line__	The current line number of the file.	1. <?Php 2. Echo __line__; // result = 2 3. Echo __line__; // result = 3
2	__file__	The full path and filename of the file.	Echo __file__; // result = "/full/path/of/this/file.php"
3	__function__	Returns the function name as it was declared (case-sensitive).	Function hellofunction() { echo __function__; } hellofunction(); // result = "hellofunction"
4	__class__	Returns the class name as it was declared (case-sensitive).	Class helloclass { public function hellomethod() { echo __class__; } } $x = new helloclass; $x->hellomethod(); // result = "helloclass"
5	__method__	Returned as it was declared (case-sensitive).	Class helloclass { public function hellomethod() { echo __method__; } } $x = new helloclass; $x->hellomethod();  // result = "helloclass::hellomethod"
6	__namespace__	Returns the name of the current namespace in use.	Namespace hellonamespace; echo __namespace__;  //result = "hellonamespace"
7	Classname::class	Returns the fully qualified class name, it is really handy when using namespaces.	Namespace hellonamespace; class helloclass { } echo helloclass::class; // result = hellonamespace\helloclass
8	__trait__	Return the name of the trait that we are currently using. It will also prepend the trait with the current namespace as well.	Namespace hellonamespace; trait hellotrait { function hellomethod() { echo __trait__; }  } class helloclass { use hellotrait; } $x = new helloclass; $x->hellomethod();  // result = "hellonamespace\hellotrait"
9	__dir__	Return the full directory path of the currently executed file.	Echo __dir__; // result = "/full/directory/path/of/file"