Re: BUG #13898: ecpg complains on nested comments in /usr/pgsql-9.4/include/informix/esql/datetime.h

On 2016-02-01 13:16:20 +0100, Michael Meskes wrote:
> > and ends on an ordinary line. I am not sure what the C standard says
> > about such cases, but I can certainly imagine that some tools might not
> > be very happy with that.
>
> We/I have to figure out what the standard says, because if it allows
> these comments, the lexer itself has to be fixed to work correctly
> instead of just fixing the header files.

The relevant translation phases are 3 and 4 according to the C standard
(section 5.1.1.2 in C11):

| 3. The source file is decomposed into preprocessing tokens7) and
| sequences of white-space characters (including comments). A source
| file shall not end in a partial preprocessing token or in a partial
| comment. Each comment is replaced by one space character. New-line
| characters are retained. Whether each nonempty sequence of
| white-space characters other than new-line is retained or replaced
| by one space character is implementation-defined.
|
| 4. Preprocessing directives are executed, macro invocations are
| expanded, and _Pragma unary operator expressions are executed. If a
| character sequence that matches the syntax of a universal character
| name is produced by token concatenation (6.10.3.3), the behavior is
| undefined. A #include preprocessing directive causes the named
| header or source file to be processed from phase 1 through phase 4,
| recursively. All preprocessing directives are then deleted.

Comments are replaced with whitespace in phase 3, preprocessing
directives are are only considered in phase 4. So code like

----------------------------------------------------------------------------
#ifndef _ECPGLIB_H /* source created by ecpg which defines these␤
* symbols */␤
----------------------------------------------------------------------------

is valid C and should be exactly equivalent to

----------------------------------------------------------------------------
#ifndef _ECPGLIB_H ␤
␤
----------------------------------------------------------------------------

(␤ denotes a newline character here)

hp

--
_ | Peter J. Holzer | I want to forget all about both belts and
|_|_) | | suspenders; instead, I want to buy pants
| | | hjp(at)hjp(dot)at | that actually fit.
__/ | http://www.hjp.at/ | -- http://noncombatant.org/