using an absolute pointer address as a template argument

Question

I have a template class which takes as its first template argument a foo * pointer. I\'d like to instantiate one of these with a foo located at an absolute address, like so:

Answer 1

Have you try casting the pointer address to and from uintptr_t, which is an unsigned integer capable of holding a pointer value? The type is defined in a standard header but it is only optional. If it does not exist in your version of C++, try size_t instead.

A full example would then look like:

#include 

class foo
{
    int baz;
};

template class bar
{
    constexpr static const foo* f = (foo*)(addr);
public:
    bar() {}
    void update() {  }
};

#define FOO_ADDR ((uintptr_t)0x80103400)

int main() {
    bar myFoo;
}

The obvious drawback is that there is no typechecking at the template parameter. You pass a value which will hopefully refer to foo object and not a different one.

Not to mention that we are in the undefined behavior world as far as the standard goes....

---

You seem to be able to compile with the line

constexpr static const foo* f = reinterpret_cast(addr);

with at least some of the compilers as well (http://coliru.stacked-crooked.com/a/5af62bedecf2d75a)

---

If your compiler rejects casting in the context of constexpr as it is ill-formed (as per Barry's comment) you can define it as a regular static const variable:

template
class bar
{
    static const foo* f;
public:
    bar() {}
    void update() {  }
};

template
const foo* bar::f = reinterpret_cast(addr);

Less ideal but solves that problem hopefully.