- PHP Tutorial
- PHP Syntax
- PHP Variables
- PHP Data Types
- PHP Constants
- PHP Operators
- PHP if elseif else statements
- PHP Switch Statement
- Arrays in PHP
- Loops in PHP
- Strings in PHP
- GET and POST in PHP
- Functions in PHP
- Cookies in PHP
- Sessions in PHP
- Include and Require in PHP
- File Opening and Reading in PHP
- File Creation and Writing in PHP
- Form Validation in PHP
- Date and Time Functions in PHP
- Validation and Sanitizing Data Via PHP Filters
- Introduction to Object Oriented Programming in PHP
- Parameterized Constructors in PHP
- Inheritance in Object Oriented PHP
- Abstract Class in PHP
- Math Functions in PHP
- Error and Exception Handling in PHP
- Reading XML data in PHP
- Reading XML Nodes/Attributes Values in PHP
- XML DOM Parser
- Sorting Arrays in PHP
- Commonly Used Array Functions in PHP
- Commonly Used String Functions in PHP
- Access Modifiers in PHP
- Variable Examination Functions in PHP
- File Upload in PHP
- PHP and AJAX
- PHP Frameworks
- Connecting PHP to MySQL
- Create Database in MySQL via PHP Script
- Drop Database in MySQL via PHP Script
- Selecting Mysql Database via PHP Script
- Create Table in MySQL via PHP Script
- Drop Table in MySQL
- Inserting Data in MySQL Table via PHP Script
- Selecting MySQL Table Data via PHP Script
- Where Clause in MySQL
- Update MySQL Table data via PHP Script
- Deleting Data From MySQL Table via PHP Script
- Sorting MySQL table data via PHP Script
- LIKE Query in MySQL
- Select Unique Data via Distinct In MySQL
- IN Operator in MySQL
- Using BETWEEN operator in MySQL
- AND/OR Operators In MySQL
- Selecting Limited records via LIMIT in MySQL
- Max and Min Functions in MySQL
- SUM and AVG Functions in MySQL
- Using COUNT Function in MySQL
- UCASE and LCASE Functions in MySQL
- GROUP BY and HAVING Clauses in MySQL
- INSERT INTO SELECT in MySQL
- DEFAULT Statement in MySQL
- Implementing Check on Table Columns
- INNER JOIN in MySQL
- LEFT JOIN in MySQL
- RIGHT JOIN In MySQL
- Implementing FULL Join in MySQL
PHP Constants
In PHP, constant is an identifier which holds a constant value. The value of constant cannot be changed while executing the script.
Syntax
Constants are declared by using define() function.
define (name, value, case-insensitive)
Name and value are mandatory parameters. Whereas, case-insensitive is an optional parameter. Its default value is false.
Characteristics of constants
- Constants do not require $ sign.
- They start with an alphabet or underscore ( _ ) and contain alphanumeric characters
- Constants are global and accessible in the entire script.
- Constants cannot be re-assigned or undefined, once they are defined.
- Constant names are conventionally defined in uppercase.
Valid and invalid constants identifiers
<?php
// Valid constant names
define("DATABASE", "Wordpress");
define("DATABASE2", "Magento");
define("DATABASE_SYMPHONY", "Symphony");
// Invalid constant name
define("3DATABASE", "Symphony");
// Valid constant name, but do not suggest as PHP my use same name as magical constant in future,
// which may break your script.
define("__DATABASE__", "Joomla");
echo DATABASE . "<br>";
echo DATABASE2 . "<br>";
echo 3DATABASE . "<br>"; // This will generate an error
echo __DATABASE__ . "<br>";
?>Download the code Run the code
const keyword
Alternatively, constant variable can be defined using const keyword.
<?php
const KH_NAME = "John";
echo "My name is " . KH_NAME;
?>Download the code Run the code
constant () Function
It is used to retrieve the value of constant. It is helpful when you know the name of constant and want to retrieve its value.
<?php
define("KH_NAME", "My name is John");
echo constant("KH_NAME");
?>Download the code Run the code
get_defined_constants() function
It will return the array of constants name and their values. It include the default constants as well as user defined constants.
<?php
define("KH_DATABASE", "Wordpress");
define("KH_USER", "John");
const KH_PASSWORD = "password";
echo "<pre>";
print_r(get_defined_constants());
echo "</pre>";
?>Download the code Run the code