setting function pointers C

Question

I have a simple question: Let's supose that I have a function called _foo.

void _foo (void *, void *, int);

Now, I want to create a new struct that holds a ponter to _foo, so:

struct _st {
    struct _st *next;
    void (*action)(void *, void *, int);
};

And then I initialize one struct _st variable:

struct _st test = {0x0, _foo};

My question is: is there a way that I can set test.action whithout being by the name of the function? I mean, a fixed address or something like?

Answer 1

test.action is a pointer you can set it to any address (numeric address e.g. 0x2000) you want, _foo is also a symbolic name for an address. However for doing that you need to keep in mind the following points:

• You should typecast it properly to suppress compiler warning/error.

• Be cautious about the undefined behavior you may invoke by accessing some address not accessible to you including dreaded SEGFAULT runtime error.

• It is always sensible to use symbolic names/constants for such assignments to help you understand your own code in future as why did you assigned it, how can you easily modify it, etc.

Answer 2

You could use an address only if you set that address through the linker. Otherwise, the name is pretty much the only reference you have to that function.