1. An API-defined callback signature where you need to use (for example) the first and third parameters, and not the second.
2. A public API function that has become deprecated and the previous behavior is emulated in a way that doesn't require all the parameters.
3. Stub/wrapper functions.
4. Init/cleanup functions for modules written to a plugin API, when all parameters passed are not needed in all cases.
5. Language binding closure/thunk functions.
Most of the uses, I think, boil down to backwards compat and fixed callback/plugin interfaces. In those cases I think an __attribute__((unused)) or void cast aren't a huge burden. I usually turn on -Wunused-parameter just in case.
1. An API-defined callback signature where you need to use (for example) the first and third parameters, and not the second.
2. A public API function that has become deprecated and the previous behavior is emulated in a way that doesn't require all the parameters.
3. Stub/wrapper functions.
4. Init/cleanup functions for modules written to a plugin API, when all parameters passed are not needed in all cases.
5. Language binding closure/thunk functions.
Most of the uses, I think, boil down to backwards compat and fixed callback/plugin interfaces. In those cases I think an __attribute__((unused)) or void cast aren't a huge burden. I usually turn on -Wunused-parameter just in case.