At a first glance, it may look like some kind of special function that returns void and takes a void*. That's totally wrong. It's actually a function that takes zero arguments, and returns function pointer, a void (*)(void*) -- that is, a pointer to a function pointer that returns void and takes a void*. The syntax actually makes a little sense if you consider the syntax for defining a variable containing such a function:
Typedefs of function pointers are weird too:
typedef void (*ptrFunc)(void*);
But I can't help to think that the following syntax would be much clearer:
void (*)(void*) f(); // invented syntax
void (*)(void*) f;
typedef void (*)(void*) ptrFunc;
These would make a lot more sense than the current function pointer syntax in C/C++, and would 'logically match' other declarations -- [return] type followed by an identifier (followed by argument list if it is a function), instead of mixing [return] type, identifier and argument list into one big mess.
It may be that the invented syntax is harder to parse -- I have thought a while on this, but haven't come to a reliable conclusion. The syntax may just be a historical artifact.
In any case, this odd syntax must be the reason why you usually define typedefs for function pointers, as done above. Then we can use the following syntax:
Much cleaner and understandable -- the obvious drawback is: what's a ptrFunc? You'll have to find the typedef to know. But I think that's worth it.