Cycling through array goes over the count of elements

Question

I have this array:

static const Layout layouts[] = {
    { "[]=",      tile },
    { "><>",      NULL },
    { "[M]",      monocle },
};

This function should cycle through the array:

int
cyclelayout(const Arg *arg) {
    static unsigned short int layout = 0;
    if (++layout >= sizeof(layouts)/sizeof(layouts[0])) {
        layout = 0;
    }
    setlayout( &((Arg) {.v = &layouts[layout]}));
}

When it is called it should set next layout or return to 0 if it goes beyond array elements. but it goes over the array elements and the program crashes. I cant figure out whats wrong?

Arg and Layout:

typedef union {
    int i;
    unsigned int ui;
    float f;
    const void *v;
} Arg;

typedef struct {
    const char *symbol;
    void (*arrange)(Monitor *);
} Layout;

Complete program: dwm-6.0 dwm-6.0-cyclelayout.patch

Answer 1

int  // This says to return an int.
cyclelayout(const Arg *arg) {
    static unsigned short int layout = 0;
    if (++layout >= sizeof(layouts)/sizeof(layouts[0])) {
        layout = 0;
    }
    setlayout( &((Arg) {.v = &layouts[layout]}));  // This doesn't look like valid C to me?

    return 4;  // http://xkcd.com/221/
}

If your function should "cycle through an array", shouldn't it have a loop somewhere?

Loops come in the flavors:

for
do-while
while

I don't see any of those keywords in your function, so I conclude it doesn't "cycle" through anything.

Answer 2

My 2 cents:

• you have an hidden if/else construct there, setLayout is part of the else clause, it's not a real error but you have something that is implicit and not readable to anyone, not explicit
• you are using a pre-increment operator ++variable which returns a reference and not a copy of the object like the post-increment operator variable++ does, it's probably not the "quantity" that you want to use in a comparison
• you are not returning any value considering that you have declared to return an int in the signature for your function

It will also help to know what is Arg and Layout as a type.