Does PHP have an equivalent of C/C++'s #ifdef?

Question

I'm trying to define a constant, but I don't want to redefine it if it's already been defined. Here's a C sample:

#ifndef BASEPATH
#define BASEPATH /mnt/www
#endif

What is the most elegant way to do this in PHP?

Answer 1

Use defined() and define().

if (!defined('BASEPATH')) {
    define('BASEPATH', '/mnt/www');
}

Answer 2

if(!defined('BASEPATH')) {
    define('BASEPATH', '/mnt/www');
}

http://us3.php.net/manual/en/function.defined.php