c - Strange behaviour of gcc in Debian

char * stft (const char *fmt, ...) {

    va_list items;
    char *out;

    int magic = 0; // <-- here magic?

    va_start (items, fmt);
    vsprintf (out, fmt, items);
    va_end (items);

    return out;

}

Use like:

char *str = stft ("%s-%s %s", a, b, c);

This is working solution?
if delete unused "magic" variable - I have Segmentation fault after return string.
What doing wrong?

$ gcc --version
gcc (Debian 4.4.5-8) 4.4.5

$ uname -a
Linux deep-station (squeeze) 2.6.32-5-686 #1 SMP Fri May 10 08:33:48 UTC 2013 i686 GNU/Linux