How can undefined constants in PHP code lead to errors and how can they be fixed?

Undefined constants in PHP code can lead to errors because PHP will interpret them as strings without quotes, causing a notice or warning to be generated. To fix this issue, you can define the constants using the `define()` function before using them in your code. 

define('MY_CONSTANT', 'my_value');

// Now you can use the constant without any issues
echo MY_CONSTANT;

Keywords

undefined constants PHP code errors fix constant defined

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