PHP Constants

Silimiar to C++, PHP use define keyword to declare a constant.

<?PHP
	define("PI",3.1415926);
	define("OOP", "Object Oriented Programming");
?>

Function constant() returns the value of a constant.

<?PHP
	echo PI; //Print 3.1415926
	echo "PI"; //Print PI
	echo constant("PI");  //Print 3.1415926
?>

PHP built in constants list:

Constant
Description
M_PI
pi, ~3.1415926535898
M_E
e, ~2.718281828459
_LINE_
Line number of current file
_FILE_
Full path name of current file
_DIR_
Directory of current file
_FUNCTION_
Name of current function
_CLASS_
Name of current class
_TRAIT_
Name of current trait
_METHOD_
Name of current class method
_NAMESPACE_
Name of current namespace
FALSE, TRUE, NULL
PHP_VERSION
current php version, also PHP_MAJOR_VERSION, PHP_MINOR_VERSION, PHP_RELEASE_VERSION, PHP_VERSION_ID, PHP_EXTRA_VERSION
PHP_MAXPATHLEN
Maximum length of filenames
PHP_OS
Current operation system
PHP_SAPI
Server API
PHP_EOL
End of Line
PHP_INT_MAX
Largest integer supported, similar PHP_INT_SIZE
DEFAULT_INCLUDE_PATH
Current PHP search path
PEAR_INSTALL_DIR
Install path of pear, similar PEAR_EXTENSION_DIR
PHP_EXTENSION_DIR
PHP extension directory
PHP_BINDIR
Directories where binaries installed, similiar PHP_MANDIR, PHP_LIBDIR, PHP_DATADIR, PHP_SYSCONFDIR, PHP_LOCALSTATEDIR, PHP_CONFIG_FILE_PATH, PHP_CONFIG_FILE_SCAN_DIR
PHP_SHLIB_SUFFIX
Shared library suffix

PHP ERROR constants:
E_ERROR, E_WARNING, E_PARSE, E_NOTICE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR, E_COMPILE_WARNING, E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE, E_DEPRECATED, E_USER_DEPRECATED, E_ALL, E_STRICT.

Adjust error reporting using the ERROR constants:

<?PHP
	error_reporting(0); //no error reporting
	error_reporting(E_ALL); //report all errors
	error_reporting(E_ALL ^ E_WARNING); //report all errors except E_WARNING
	error_reporting(E_ERROR | E_WARNING); //report E_ERROR and E_WARNING
?>

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