Define Constant PHP

Constant in PHP ?

Constant are identifiers for a memory location Which Can be change according to requirement of program .In PHP Constant does NOT support interpolation . In PHP Constant must be in Upper Case eg. CONST  .To define Constant we have to use function define();

Syntax :

define(‘name of constant ‘,’ value of constant’)
eg: define(‘PIE’,’3.14′);
echo PIE;/// will result to 3.14

NOTE:Unlike variable  If we Try to define same Constant again then it throw a notice Already define.


Another way of Defining Constant is key word const .

eg:  const MIN_VALUE = 0.0;

echo   MIN_VALUE ; /// will result to 0


The fundamental difference between those two ways is that const defines constants at compile time, whereas define defines them at run time.

Note : const cannot be used to conditionally define constants. It has to be used in the outermost scope



$x=10 and $y=10;
if ($x==$y) {
const CONST_VAL1 = ‘CONST’; // invalid produce error
// but
if ($x==$y) {
define(‘CONST_VAL2’, ‘CONST’); // valid
echo CONST_VAL1; // produce error
echo CONST_VAL2;