How can undefined constant errors be resolved in PHP code?

Undefined constant errors in PHP code can be resolved by ensuring that constants are properly defined with the define() function or by using the correct syntax when accessing predefined constants. If a constant is being treated as a string without quotes, PHP will throw an undefined constant error. To fix this, enclose the constant name in quotes to treat it as a string. 

// Incorrect usage causing undefined constant error
echo FOO;

// Correct usage
define('FOO', 'bar');
echo FOO;

Keywords

PHP constant error define define()

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