What is the simplest standard conform way to produce a Segfault in C?

Question

I think the question says it all. An example covering most standards from C89 to C11 would be helpful. I though of this one, but I guess it is just undefined behaviour:

#include <stdio.h>

int main( int argc, char* argv[] )
{
  const char *s = NULL;
  printf( "%c\n", s[0] );
  return 0;
}

EDIT:

As some votes requested clarification: I wanted to have a program with an usual programming error (the simplest I could think of was an segfault), that is guaranteed (by standard) to abort. This is a bit different to the minimal segfault question, which don't care about this insurance.

Answer 1

A segmentation fault is an implementation defined behavior. The standard does not define how the implementation should deal with undefined behavior and in fact the implementation could optimize out undefined behavior and still be compliant. To be clear, implementation defined behavior is behavior which is not specified by the standard but the implementation should document. Undefined behavior is code that is non-portable or erroneous and whose behavior is unpredictable and therefore can not be relied on.

If we look at the C99 draft standard §3.4.3 undefined behavior which comes under the Terms, definitions and symbols section in paragraph 1 it says (emphasis mine going forward):

behavior, upon use of a nonportable or erroneous program construct or of erroneous data, for which this International Standard imposes no requirements

and in paragraph 2 says:

NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message).

If, on the other hand, you simply want a method defined in the standard that will cause a segmentation fault on most Unix-like systems then raise(SIGSEGV) should accomplish that goal. Although, strictly speaking, SIGSEGV is defined as follows:

SIGSEGV an invalid access to storage

and §7.14 Signal handling <signal.h> says:

An implementation need not generate any of these signals, except as a result of explicit calls to the raise function. Additional signals and pointers to undeclarable functions, with macro definitions beginning, respectively, with the letters SIG and an uppercase letter or with SIG_ and an uppercase letter,219) may also be specified by the implementation. The complete set of signals, their semantics, and their default handling is implementation-defined; all signal numbers shall be positive.