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PHP Manual :: Class Constants



Properties || Autoloading Classes || Classes and Objects || PHP Manual

It is possible to define constant values on a per-class basis remaining the same and unchangeable. Constants differ from normal variables in that you don't use the $ symbol to declare or use them.

The value must be a constant expression, not (for example) a variable, a property, or a function call.

It's also possible for interfaces to have constants. Look at the interface documentation for examples.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

Example #1 Defining and using a constant

<?php
class MyClass
{
    const 
CONSTANT 'constant value';

    function 
showConstant() {
        echo  
self::CONSTANT "\n";
    }
}

echo 
MyClass::CONSTANT "\n";

$classname "MyClass";
echo 
$classname::CONSTANT "\n"// As of PHP 5.3.0

$class = new MyClass();
$class->showConstant();

echo 
$class::CONSTANT."\n"// As of PHP 5.3.0
?>

Example #2 Static data example

<?php
class foo {
    
// As of PHP 5.3.0
    
const BAR = <<<'EOT'
bar
EOT;
    
// As of PHP 5.3.0
    
const BAZ = <<<EOT
baz
EOT;
}
?>

Note:

Support for initializing constants with Heredoc and Nowdoc syntax was added in PHP 5.3.0.

Example #3 Constant expression example

<?php
const ONE 1;

class 
foo {
    
// As of PHP 5.6.0
    
const TWO ONE 2;
    const 
THREE ONE self::TWO;
    const 
SENTENCE 'The value of THREE is '.self::THREE;
}
?>

It is possible to provide a scalar expression involving numeric and string literals and/or constants in context of a class constant.

Note:

Constant expression support was added in PHP 5.6.0.



Properties || Autoloading Classes || Classes and Objects || PHP Manual
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