Switch case on an enum that is never changed

Question

I came across the following code and can't seem to understand what's going on here. The enum pattern is never changed so why do a switch on it?

enum pattern { PAT_ZERO, PAT_SEQ, PAT_PIPE };
static enum pattern pattern;

static ssize_t fill_in_buf(struct thread *ignore, void *buf, size_t nbytes)
{
    size_t i;
    __u8 *p;

    (void)ignore;

    switch (pattern) {
    case PAT_ZERO:
        printf("fill_in_buf PAT_ZERO\n");
        memset(buf, 0, nbytes);
        break;

    case PAT_SEQ:
        printf("fill_in_buf PAT_SEQ\n");
        for (p = buf, i = 0; i < nbytes; ++i, ++p)
            *p = i % 63;
        break;

    case PAT_PIPE:
        printf("fill_in_buf PAT_PIPE\n");
        return fread(buf, 1, nbytes, stdin);
    }

    return nbytes;
}

Are you sure? The code is from http://lxr.free-electrons.com/source/tools/usb/ffs-test.c#L362 — tzippy, Jan 30 '14 at 14:07
@tzippy: Because some code somewhere else changes the value of `pattern`? — Jon, Jan 30 '14 at 14:08
@self. I didn't try it... may be correct.. can you explain a bit more — Grijesh Chauhan, Jan 30 '14 at 14:08
@Dayalrai It is static, I don't see how. THe code must be a test( name:ffs-test.c) therefore it is there to check the values and is changed by hand if needed. — this, Jan 30 '14 at 14:10
@tzippy No I saw you link I will learn about it. Thanks! ..I should remove the comment.. — Grijesh Chauhan, Jan 30 '14 at 14:12
@self. That's actually the only possibility that makes sense, yes. — tzippy, Jan 30 '14 at 14:15
@Dayalrai You're wrong, http://stackoverflow.com/a/4576643/2327831 — this, Jan 30 '14 at 14:43

score 0 · Answer 1 · answered Jan 30 '14 at 14:42

It looks like test/debugging code, the programmer wanted a few varieties to choose from.

It's quite unexpectedly written, typically you'd see this done with the preprocessor and #if defined to choose one code path.

The two first lines could be clarified to:

static const enum { PAT_ZERO, PAT_SEQ, PAT_PIPE } pattern = PAT_ZERO;

Since there's no point in introducing a name for the enum, or making the variable non-const.

Switch case on an enum that is never changed

1 Answers1