What signal is generated from (int )0='X';

Question

What exactly does the following do (or try to do) in C?

*(int *)0='X';

And what signal would be generated? Would it be a SIGSEGV?

Yes, on most POSIX systems you'll get a SIGSEGV. P.S. -- any particular reason you couldn't compile this, and test it yourself? — Sam Varshavchik, Dec 11 '15 at 13:42
To generate signals you must generate them explicitly. Undefined behavior is not reliable for that. — Iharob Al Asimi, Dec 11 '15 at 13:42
Perhaps related to [What does “*((char*)-1) = 'x';” code mean?](http://stackoverflow.com/q/20844863/1708801) — Shafik Yaghmour, Dec 11 '15 at 13:43
@SamVarshavchik maybe he was forced to use losedows for a while? — sadljkfhalskdjfh, Dec 11 '15 at 13:46
@SamVarshavchik Testing is not a suitable way to get definite answers about what the C language specifies. Undefined behaviour has the annoying habit of allowing anything to happen. — fuz, Dec 11 '15 at 14:20
I would load the reset vector with an int representation of the character 'W'. Nothing else would happen, (on my embedded board). — Martin James, Dec 11 '15 at 14:30
@Martin James I see - the result is hardXare dependent. At least you didn't type "chuw". ;-) — chux - Reinstate Monica, Dec 11 '15 at 14:51

score 3 · Answer 1 · answered Dec 11 '15 at 13:47

The behaviour of *(int *)0='X'; is undefined.

The compiler is free to do anything it pleases. (i) raise a SIGSEGV, (ii) not compiling the line at all are two possibilities.

To generate a fault explicitly, use raise as appropriate (defined in <signal.h>).

score 0 · Answer 2 · answered Dec 11 '15 at 13:44

Putting this into a complete program, segv.c:

int
main(
    void)
{
    *(int *) 0 = 'X';
    return 0;
}

and compiling:

clang -Oz -Wno-error -s -o segv segv.c

Now, when I run it on my 64-bit GNU/Linux system, I do in fact get a segmentation fault:

fish: "./segv" terminated by signal SIGSEGV (Address boundary error)

However, if you are seeking to generate segmentation faults, as some people in comments have pointed out, you should use raise(3) from signal.h.

What signal is generated from *(int *)0='X';