PHP, Structures and Functions, Fundamental Syntaxes

This function is useful if you need to retrieve the value of a constant, but do not know its name; that is, it is stored in a variable or returned by a function.

This function allows another way to show a CONSTANT value.

If the $name is not defined an E_WARNING level error or NULL is generated.


<?php

mix constant ( str $name )



where,

$name = The constant name

?>

$name

The name of the CONSTANT to print the value.

EXERCISE


<?php

define ('PI', M_PI);

echo 'The value of the defined constant is:<br>';

echo 'PI = ' . constant("PI");

?>

RESULT

The value of the defined
for this INTERNAL constant is:
PI = 3.1415926535898

EXERCISE


<?php

$path = "PATH2VERA";

echo 'The path to the character set VERA is:<br>';

echo constant($path);

?>

RESULT

The path to the character set VERA character set is:

H:\\...\ttf\vera

Constant value assigned to the path to Vera.

Just for example.

EXERCISE


<?php

$arr = [ 1, 2, 3, 'a',  'c'];

echo 'The currently defined constant is:<br>';

var_dump(constant($arr));

?>

RESULT

In PHP 7.4.XX it displays a Warning message, but in PHP 8.0.XX it displays a Fatal error.

EXERCISE


<?php

define('A', 'AÂÂÁÀ');

echo 'The currently defined constant is:<br>';

var_dump(constant('A'));


/* - - - - - - - - - - - - - - - - - - - - -
   Accented letters count 
   as having two characters.
   - - - - - - - - - - - - - - - - - - - - - */

?>

EXERCISE


<?php

define ("P205a", $_SERVER['DOCUMENT_ROOT'] . '/adds/');

define ("P205b", 'file://' . $_SERVER['DOCUMENT_ROOT'] . '/adds/');

define ("P205c", $_SERVER['DOCUMENT_ROOT'] . '/temp/');

$arr05 = [ 'P205a', 'P205b', 'P205c' ];
  
print_r($arr05);

echo '<br><br>' . constant($arr05[0]);

echo '<br><br>' . constant($arr05[1]);

echo '<br><br>' . constant($arr05[2]);


?>