Why is this an issue?

In PHP, the define function allows you to define a named constant with a specific value, which cannot be changed later in the code. Once a constant has been defined, it can be used throughout the entire script, including in function and class definitions.

Assigning a value to the same constant name using two or more define statements does not cause PHP to fail. In such a case, PHP only issues a warning and ignores the second and further define.

What is the potential impact?

Using duplicate define statements can lead to unnecessary code that can be safely removed in the best case scenario.

It is important to note that in the worst case, duplicate define statements may assign different values, which can result in hard-to-debug issues when other parts of the code make incorrect assumptions about the constant’s value.

It is advisable to avoid duplicate define statements to prevent potential unexpected behavior and to ensure code clarity and correctness.

How to fix it

Remove duplicate define statements and only keep the intended one.

Code examples

Noncompliant code example

define( 'CONSTANT_VALUE', 'old value' );
define( 'SCRIPT_DEBUG', 1 );

// Noncompliant, tries to redefine constant defined 2 lines above
define( 'CONSTANT_VALUE', 'intended value' );
echo CONSTANT_VALUE; // output: 'old value'

Compliant solution

define( 'SCRIPT_DEBUG', 1 );

// Compliant
define( 'CONSTANT_VALUE', 'intended value' );
echo CONSTANT_VALUE; // output: 'intended value'

Resources

Documentation