Printing null pointers with %p is undefined behavior?

Question

Is it undefined behavior to print null pointers with the %p conversion specifier?

#include 

int main(void) {
    void *p = NULL;

           


        

Answer 1

The authors of the C Standard made no effort to exhaustively list all of the behavioral requirements an implementation must meet to be suitable for any particular purpose. Instead, they expected that people writing compilers would exercise a certain amount of common sense whether the Standard requires it or not.

The question of whether something invokes UB is seldom in and of itself useful. The real questions of importance are:

1. Should someone who is trying to write a quality compiler make it behave in predictable fashion? For the described scenario the answer is clearly yes.

2. Should programmers be entitled to expect that quality compilers for anything resembling normal platforms will behave in predictable fashion? In the described scenario, I would say the answer is yes.

3. Might some obtuse compiler writers stretch the interpretation of the Standard so as to justify doing something weird? I would hope not, but wouldn't rule it out.

4. Should sanitizing compilers squawk about the behavior? That would depend upon the paranoia level of their users; a sanitizing compiler probably shouldn't default to squawking about such behavior, but perhaps provide a configuration option to do in case programs might be ported to "clever"/dumb compilers that behave weirdly.

If a reasonable interpretation of the Standard would imply a behavior is defined, but some compiler writers stretch the interpretation to justify doing otherwise, does it really matter what the Standard says?