Possible Duplicate:
Why are function pointers and data pointers incompatible in C/C++?
In the man page for dlsym, the following snippet has been provided.
double (*cosine)(double);
handle = dlopen("libm.so", RTLD_LAZY);
/* Writing: cosine = (double (*)(double)) dlsym(handle, "cos");
would seem more natural, but the C99 standard leaves
casting from "void *" to a function pointer undefined.
The assignment used below is the POSIX.1-2003 (Technical
Corrigendum 1) workaround; see the Rationale for the
POSIX specification of dlsym(). */
*(void **) (&cosine) = dlsym(handle, "cos");
I looked up the relevant spec page, but still cannot grasp the reason behind not allowing conversions from void pointers to function pointers. Aren't void pointers supposed to be big enough to accomodate all types of pointers. If so, why leave this casting undefined?
