How to correctly assign a pointer returned by dlsym into a variable of function pointer type?

Question

I am trying to use dlopen() and dlsym() in my code and compile it with gcc.

Here is the first file.

/* main.c          


        

Answer 1

If you want to be pedantically correct, don't try to resolve the address of a function. Instead, export some kind of structure from the dynamic library:

In the library

struct export_vtable {
   void (*helloworld)(void);
};
struct export_vtable exports = { func };

In the caller

struct export_vtable {
   void (*helloworld)(void);
};

int main() {
   struct export_vtable* imports;
   void *handle = dlopen("./foo.so", RTLD_NOW);

   if (handle) {
        imports = dlsym(handle, "exports");
        if (imports) imports->helloworld();
    }

    return 0;
}

This technique is actually quite common, not for portability -- POSIX guarantees that function pointers can be converted to and from void* -- but because it allows more flexibility.