Thread: Is this not undefined behavior?

I was looking through the winpcap documentation and noticed this bit of code...

Code:

/* From tcptraceroute, convert a numeric IP address to a string */
#define IPTOSBUFFERS    12
char *iptos(u_long in)
{
    static char output[IPTOSBUFFERS][3*4+3+1];
    static short which;
    u_char *p;

    p = (u_char *)∈
    which = (which + 1 == IPTOSBUFFERS ? 0 : which + 1);
    _snprintf_s(output[which], sizeof(output[which]), sizeof(output[which]),"%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
    return output[which];
}

local variable "which" is not initialized. Unless I'm missing something that's undefined behavior. Or is there some sort of trickery going on here that I'm not aware of? There's an evaluation of it yet that variable could contain anything during that first go around (or any after for that matter).

local variable "which" is not initialized. Unless I'm missing something that's undefined behavior.

Yes you're missing something. Both static and global variables are initialized to zero by default.

Jim

Well I know one thing, if it goes uninitialized, it will get the values left on the stack. Which is usually something abnormal like -344643.

But static variables don't go uninitialized, they wil be initialized to zero.

Jim

Also static variable aren't on the stack, instead they are in the data portion of a program. There's only one instance of each static variable, from the start of a program until the program ends.