defined

defined

(PHP 4, PHP 5)

definedChecks 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

if (defined('TEST')) {
    echo 
TEST;
}
?>

参见


  • connection_aborted
  • connection_status
  • connection_timeout
  • constant
  • define
  • defined
  • die
  • eval
  • exit
  • highlight_file
  • highlight_string
  • ignore_user_abort
  • pack
  • php_check_syntax
  • php_strip_whitespace
  • show_source
  • sleep
  • sys_getloadavg
  • time_nanosleep
  • time_sleep_until
  • uniqid
  • unpack
  • usleep
  • __halt_compiler
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