Question

I have been implementing a user threads library as part of my assignment.
I didn’t understand the makecontext function:

makecontext(&(mainthread->threadctx),(void(*)(void))start_funct,1,args)

What does (void(*)(void))start_funct exactly mean? And why do I have to write it this way?
Can’t I just write it as

makecontext(&(mainthread->threadctx),start_funct,1,args) ?

Please be patient with me, I am not yet comfortable with pointers 🙂

Answer 1

void(*)(void) means “pointer to a function that takes no parameters and returns void“.

Therefore (void(*)(void))start_funct is casting start_funct (which we can assume is some kind of function pointer)` to the above type. (There is a very useful online tool that can help you with this until you get more comfortable reading declarations).

You have to write it this way because the signature of start_funct is not void start_funct(void), so casting is required.