Casting Void Pointers to Function Pointers in C

Converting void pointers returned by functions like dlsym() to function pointers is not straightforward in C . By default, such direct casting is prohibited in C 98/03.

Reason for Restriction

In C 98/03, void* pointers were intended for referencing objects, not function or member pointers.

Conditional Support in C 0x

In C 0x, casting void* to function pointers is optionally supported by implementations. If supported, the behavior must conform to the standard.

Implementation-Dependent Workarounds

While direct casting is not allowed, these workarounds may function on most platforms:

• Reinterpret Cast:

fptr my_fptr = reinterpret_cast(reinterpret_cast(gptr));

• Variable Reinterpretation:

fptr my_ptr = 0;
reinterpret_cast(my_ptr) = gptr;

These workarounds exploit the fact that function pointer addresses are objects and can be converted to void** pointers using reinterpret_cast.

Cautionary Note

These workarounds involve undefined behavior and should be used with discretion.