#define COMMAND_STEP 1234
struct command_step {
 int kind;
 int size;
};

#define MACROTABLE(ID,NAME,...) \
 static const int COMMAND_##NAME = ID; \
 struct command_##NAME { \
  __VA_ARGS__ \
 }; \
 static const int COMMAND_##NAME##_sizeof = sizeof(command_##NAME);

MACROTABLE(1234, step,
 int kind;
 int size
);

-->

static const int COMMAND_step = 1234;
struct command_step {
 int kind;
 int size;
};
static const int COMMAND_step_sizeof = 8;