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# function_exists

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

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

## Description

``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().

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