defined

(PHP 4, PHP 5)

defined — Checks whether a given named constant exists

说明

bool defined ( string $name )

Checks whether the given constant exists and is defined.

Note: If you want to see if a variable exists, use isset() as defined() only applies to constants. If you want to see if a function exists, use function_exists().

参数

name: The constant name.

返回值

Returns TRUE if the named constant given by name has been defined, FALSE otherwise.

范例

Example#1 Checking Constants


<?php
/* Note the use of quotes, this is important.  This example is checking
 * if the string 'CONSTANT' is the name of a constant named CONSTANT */
if (defined('CONSTANT')) {
    echo CONSTANT;
}
?>

参见

define()
constant()
get_defined_constants()
function_exists()
The section on Constants


	PHP5中文手册 define die Misc. PHP Manual defined (PHP 4, PHP 5) defined — Checks whether a given named constant exists 说明 bool defined ( string `$name` ) Checks whether the given constant exists and is defined. Note: If you want to see if a variable exists, use isset() as defined() only applies to constants. If you want to see if a function exists, use function_exists(). 参数 `name` The constant name. 返回值 Returns `TRUE` if the named constant given by `name` has been defined, `FALSE` otherwise. 范例 Example#1 Checking Constants `<?php /* Note the use of quotes, this is important. This example is checking * if the string 'CONSTANT' is the name of a constant named CONSTANT */ if (defined('CONSTANT')) { echo CONSTANT; } ?>` 参见 define() constant() get_defined_constants() function_exists() The section on Constants define die Misc. PHP Manual