function_exists — Return TRUE if the given function has been defined
Description
boolfunction_exists
( string$function_name
)
Checks the list of defined functions, both built-in (internal) and
user-defined, for function_name
.
Parameters
function_name
The function name, as a string.
Return Values
Returns TRUE if function_name
exists and is a
function, FALSE otherwise.
Note:
This function will return FALSE for constructs, such as
include_once() and echo().
Examples
Example #1 function_exists() example
<?php if (function_exists('imap_open')) { echo "IMAP functions are available.<br />\n"; } else { echo "IMAP functions are not available.<br />\n"; } ?>
Notes
Note:
A function name may exist even if the function itself is unusable due to
configuration or compiling options (with the image functions being an example).
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