Re: NULL passed as an argument to memcmp() in parse_func.c

On 06/23/2015 06:42 PM, Tom Lane wrote:
> Glen Knowles <gknowles@ieee.org> writes:
>> It appears that, according to the standard, passing NULL to memcmp is
>> undefined behavior, even if the count is 0. See
>> http://stackoverflow.com/questions/16362925/can-i-pass-a-null-pointer-to-memcmp
>> for C99 and C++ standard references.
>
> Hmm ... looks like that's correct.  I had not noticed the introductory
> paragraphs.  For those following along at home, the relevant text in
> C99 is in "7.21.1 String function conventions":
>
>         [#2]  Where  an  argument declared as size_t n specifies the
>         length of the array for a function, n  can  have  the  value
>         zero  on  a call to that function.  Unless explicitly stated
>         otherwise in the description of  a  particular  function  in
>         this subclause, pointer arguments on such a call shall still
>         have valid values, as described in 7.1.4.  On such a call, a
>         function  that  locates  a  character finds no occurrence, a
>         function that compares two character sequences returns zero,
>         and   a   function   that   copies  characters  copies  zero
>         characters.
>
> and the relevant text from 7.1.4 is
>
>         [#1]   Each  of  the  following  statements  applies  unless
>         explicitly stated otherwise  in  the  detailed  descriptions |
>         that  follow:  If  an  argument to a function has an invalid
>         value (such as a value outside the domain of  the  function,
>         or  a pointer outside the address space of the program, or a
>         null pointer) or a type (after promotion) not expected by  a
>         function  with variable number of arguments, the behavior is
>         undefined.

For what it's worth, in C89 and C90 the wording of the latter paragraph 
(respectively 4.1.6 and 7.1.7) is:

> Use of library functions
> Each of the following statements applies unless explicitly stated
> otherwise in the detailed descriptions that follow. If an argument to
> a function has an invalid value (such as a value outside the domain
> of the function, or a pointer outside the address space of the
> program, or a null pointer), the behavior is undefined. [...]