如何在PHP中回显定义值？

My code is here:

<?php define("SITENAME","Page TITLE");?>

I want to echo define value like:

<?php echo "<?=SITENAME?>";?>

Would someone tell me how?

Here you go:

<?php 
    define("SITENAME","Page TITLE");    
    echo "My website title: ".SITENAME; 
?>

output : My website title: Page TITLE

You can echo the value of constant as below

define("SITENAME","Page TITLE");
echo SITENAME.': My New Content Here';

This gives : Page TITLE: My New Content Here

For more reference:

define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.

define("GREETING", "Hello you.", true);
echo GREETING; // outputs "Hello you."
echo Greeting; // outputs "Hello you."

// Works as of PHP 7
define('ANIMALS', array(
    'dog',
    'cat',
    'bird'
));
echo ANIMALS[1]; // outputs "cat"