In this PHP tutorial, we will learn how to list the constants used in our PHP program. And we will show example which prints the all constants defined.

• PHP constants defined can be listed using the function get_defined_constants().
• get_defined_constants() returns the system defined and user defined constants in associative array form.

Example of PHP list Constants
<?php
    define("g",9.8);
    define("PI",31.4);
    $cons=get_defined_constants();
    echo"<pre>";
    foreach ($cons as $key=>$val)
      {
      echo"<br>$key=>$val ";
      }
    echo "</pre>";
?>
Output

E_ERROR=>1
E_RECOVERABLE_ERROR=>4096
E_WARNING=>2
E_PARSE=>4
TRUE=>1
FALSE=>
NULL=>
ZEND_THREAD_SAFE=>1
PHP_VERSION=>5.2.9
PHP_MAJOR_VERSION=>5
PHP_MINOR_VERSION=>2
PHP_RELEASE_VERSION=>9
UPLOAD_ERR_OK=>0
UPLOAD_ERR_INI_SIZE=>1
UPLOAD_ERR_FORM_SIZE=>2
UPLOAD_ERR_PARTIAL=>3
CAL_GREGORIAN=>0
CAL_JULIAN=>1
CAL_JEWISH=>2
CAL_FRENCH=>3
CAL_NUM_CALS=>4
VT_NULL=>1
VT_EMPTY=>0
VT_UI1=>17
VT_I1=>16
VT_UI2=>18
FILTER_FLAG_NONE=>0
FILTER_REQUIRE_SCALAR=>33554432
FILTER_REQUIRE_ARRAY=>16777216
FILTER_FORCE_ARRAY=>67108864
g=>9.8
PI=>31.4

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