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# function_exists

(PHP 3>= 3.0.7, PHP 4 )

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

## Description

bool function_exists ( string function_name)

Checks the list of defined functions, both built-in (internal) and user-defined, for `function_name`. Returns `TRUE` on success or `FALSE` on failure.

    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 (with the image functions being an example). Also note that function_exists() will return `FALSE` for constructs, such as include_once() and echo().

See also method_exists() and get_defined_functions().

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