check integer constants have different values at compilation time

Question

My question is the following. I have a large number of static const integers that work as Identifiers. For this reason I would like to know if it is possible to check at compilation time if there is more than one constant with the same value (some kind of static assert...).

I do not want to use an enum as these constants are defined in different modules and I don't want to have like a very long enum with all of them (and some of them are not related to each other).

Here you have a basic example:

// module: foo.h
const uint32_t ELEMENT_TYPE_FOO_X = 46;
const uint32_t ELEMENT_TYPE_FOO_Y = 51;
...

// module: boo.h
const uint32_t ELEMENT_TYPE_BOO_C = 21;
const uint32_t ELEMENT_TYPE_BOO_D = 51;

error: ELEMENT_TYPE_FOO_Y and ELEMENT_TYPE_BOO_D have the same value.

I'm not an expert at all and the only thing that comes to my mind to detect this error is template specialization.

template<uint32_t N>
struct element_traits {
};

template<ELEMENT_TYPE_FOO_X> {
    enum { value = ELEMENT_TYPE_FOO };
};

But it seems to be a complex solution. I don't know if there is a more elegant/better solution. I haven't found anything so far.

Thanks in advance.

Answer 1

You could certainly do this using macros:

#define UNIQUE_CONSTANT(variable, value) \
  const uint32_t variable = value; \
  bool constant_val_##value = value;

Then you will get a multiple definition error if the same value is used twice.

(Technically, this will detect the error at link time, not compile time.)