6.6.4.1.22 -Wunused

Warn whenever a variable is unused aside from its declaration, whenever a function is declared static but never defined, whenever a label is declared but not used, and whenever a statement computes a result that is explicitly not used.

In order to get a warning about an unused function parameter, both -W and -Wunused must be specified.

Casting an expression to void suppresses this warning for an expression. Similarly, the unused attribute suppresses this warning for unused variables, parameters and labels.