Re: Help in c pointers

On 2006-02-28, Pedro Graca <hexkid@xxxxxxxxxxx> wrote:
Jordan Abel wrote:
On 2006-02-28, Kenneth Brody <kenbrody@xxxxxxxxxxx> wrote:
"manochavishal@xxxxxxxxx" wrote:
int *p;
*p = 4;

char * msg;
*msg = 'c';

printf("msg is %s",msg);

Neither pointer has been initialized, and both assignments invoke UB.

Incidentally, there's a third instance of undefined behavior here -
anyone know what it is?

a) `msg' isn't (*) a c-string (a sequence of chars ending in NUL) so
passing it to printf invokes UB.

Not quite - msg isn't a valid pointer at all, so the act itself of
passing it to printf invokes UB. It would equally invoke UB if it were a
void * and being passed to a printf %p format.

The value of msg is indeterminate since it is never initialized. Reading
an indeterminate value results in undefined behavior [since it may be a
trap representation]
.

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