Thread: To store a function's address as an integer

I have a struct

Code:

typedef struct
{
    uint8_t type;
    uint8_t num;
    uint8_t id;

    int value;
}EXPR;

the value field is a quite multipurpose one (depending on type). one of the purposes I want to use is to store a function's address.

The only way I found to do it

Code:

EXPR expr;

int(*fp)(void);
fp = Foo;
expr.value = (int)fp;

But how can I invoke the function?
With the "proper" pointer I could do

Code:

result = fp();

the question - can I inform a compiler that value is a function's address?

You could make a union out of it.

Code:

typedef struct
{
    uint8_t type;
    uint8_t num;
    uint8_t id;
    union { 
        int value;
        int (*fp)(void);
    }v;
}EXPR;

Then assign with either

Code:

EXPR var;
var.v.value = 42;
var.v.fp = Foo;

If you know it's a function, then you can just use it as a function.

Code:

result = var.v.fp();