问题
The man page of dlsym() lists
*(void **) (&cosine) = dlsym(handle, "cos");
as a workaround for casting the return value of dlsym().
What's the meaning of *(void **) (&cosine) here? I understand cosine is a function pointer defined previously, but I'm not sure why an ampersand & is needed before the name (an error without &). Moreover, I don't figure out why the pointer of void * (void **) is again used with *.
回答1:
Let's unwrap it a bit at a time:
&cosine
This takes a pointer to the variable cosine, so this will be a pointer to a function pointer.
(void **) &cosine
We cast the pointer-to-function-pointer to pointer-to-pointer-to-void.
* (void **) &cosine
We dereference the casted pointer, assigning the result of dlsym() into it.
Effectively, what's happening is a side-step of the issue. Instead of casting the result of dlsym() into the correct type of function pointer, we pretend that cosine is a void * (through a level of indirection) and assign to it.
来源：https://stackoverflow.com/questions/43509159/dlsym-workaround-return-type