Question

typedef enum {
  TYPE_A = 0,
  TYPE_B,
  TYPE_C
} OBJTYPE;

Assume there is the enum type above.
I’m using arm-g++ for my working.

And some macro for any type is defined like this:

#define ANY_TYPE ((OBJTYPE)-1)

But following comparision was false as I tested:

if (param->type == ANY_TYPE) something();
else error();

param->type was set as ANY_TYPE and its type was OBJTYPE. I logged both of them with ‘%d’ and they were displayed as 255. But it’s false and error occurred.

This problem has been not caused from RVCT (commercial arm compiler).
Why does it fail?

Answer 1

-1 is an illegal value for your enumeration.

The language standard (7.2 Enumeration declarations) says:

For an enumeration where
e_min is the smallest
enumerator and e_max is the
largest, the values of the enumeration
are the values of the underlying type
in the range b_min to
b_max, where b_min
and b_max are, respectively,
the smallest and largest values of the
smallest bit-field that can store
e_min and e_max.

According to this, legal values are 0, 1, 2 and 3 (those values that can be represented with two bits). You should add the ANY_TYPE enumerator to use it.