Array size of enum length gives compilation error

Question

Have a look at the code below,

This code compiles fine:

enum ids {
    X,
    Y,
    NUM_IDS,
}

void some_func(void)
{
    static char* const names[NUM_IDS] = { "name X" , "name Y"};
}

However this code doesn't compile: error: storage size of 'names' isn't constant

enum ids {
    X,
    Y,
    NUM_IDS,
}

void some_func(void)
{
    int nr_names = NUM_IDS;
    static char* const names[nr_names] = { "name X" , "name Y"};
}

I think I misunderstood the meaning of a constant expression. Is it the case that in second way it is becoming a VLA which is not present in C90? Somebody please clarify.

Answer 1

static char* const names[nr_names] is a VLA because nr_names isn't a constant expression, but a (non-const) int. Sure, in this short example it's always equal to NUM_IDS, but you still can't do that.

---

On an unrelated side note, it is recommended that the char is defined as const, as modifying it won't work because it's part of the program's binary (in C++ it wouldn't let you have it non-const):

static const char* const names[NUM_IDS] = { "name X" , "name Y" };