PHP constant Definition

PHP constant definitions and value constants are assigned when defined, cannot be changed, cannot be destroyed, have super-global action, and constants can only store scalar data (character integer float);

<? PHP Define ("Hello", "World");// variable name Hello  variable valueWorldecho// variable output echo "<br/ > ";

$b = constant (' hello ');//Use function constant ();
echo $b;? >

Determine if a constant exists

<? PHP if (defined("Hello")) // determine if a constant exists  defined ("Constant name")  returns True{    echo ' constant already exists! ";} Else {    echo ' constant does not exist! ";}? >

Pre-defined constants in PHP

M_PI: The constant value of pi;

Running operating system where the php_os:php is located

The version number of the php_varsion:php;

And so on and read the manual;

Magic Constants in PHP (no constant meaning values will change)

_file_: Represents the full physical path of the current web page

_dir_: Represents the folder where the current page is located

PHP constant Definition