Question

How to check whether constant exists (already defined) in PHP

Answer 1

if (defined('PI')) 
    echo PI;
else
    echo "PI is not defined";
 
/*
run: 

PI is not defined 

*/

 

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Answer 2

define("PI", 3.14);

if (defined('PI')) 
    echo PI;
else
    echo "PI is not defined";
 
/*
run: 

3.14 

*/

 

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