(3.0.7 - 3.0.18 only, PHP 4 >= 4.0.0)

function_exists --  Return TRUE if the given function has been defined


bool function_exists (string function_name)

Checks the list of defined functions for function_name. Returns TRUE if the given function name was found, FALSE otherwise.

if (function_exists('imap_open')) {
    echo "IMAP functions are available.<br>\n";
} else {
    echo "IMAP functions are not available.<br>\n";

Note that a function name may exist, even if the function itself is unusable due to configuration or compiling options.

See also method_exists().