Question

There is a function which takes a function pointer argument of the form void *(*func)(void *) and I am reading some code which calls it with the following argument (void *(*)(void *))(-1).

Is this just casting -1 to the correct function pointer type or is it something else? I am unsure of what it means.

Answer 1

Yes, that’s just a typecast. Without seeing the code in context, it’s not really possible to decide why someone might be doing that, though. It’s often convenient to use cdecl to answer questions like this one:

$ cdecl
Type `help' or `?' for help
cdecl> explain (void *(*)(void *))
cast unknown_name into pointer to function (pointer to void) returning pointer to void