[Flex-devel] #include <unistd.h> in middle of scanner: bad idea

[Kaz K. <938...@ky...>]

Hi,

I'd like to report a sort of bug.

Flex generates a file which contains
a #include <unistd.h> long after user material. This seems to be for
the sake of having a declaration of isatty.

The problem with this is that the user code can #define macros that
can break the header. C programs have to be careful with what they
do before system headers are included.

The programmer typically places #include's in the %{ %} section,
and then the assumption is that those are all the headers there are.

Here is small repro test case:

   %{

   #define pause blah[]

   %}

   %%

Result:

   $ flex lex.l ; cc lex.yy.c
   lex.l:3:15: error: declaration of ‘blah’ as array of functions
   #define pause blah[]

I understand that the directive can be suppressed with YY_NO_UNISTD_H,
but that's a workaround discovered after things break.

How about just an "extern int isatty(int)" somewhere?

Or just plant it in this section:

   /* First, we deal with  platform-specific or compiler-specific issues. 
*/

   /* begin standard C headers. */
   #include <stdio.h>
   #include <string.h>
   #include <errno.h>
   #include <stdlib.h>
   #ifndef YY_NO_UNISTD_H
   #include <unistd.h>
   #endif

   /* end standard C headers. */

If you're going to include <unistd.h> eventually, why beat around the
bush; clump it with other system headers.

If someone wants to disable that, they can use flex --nounistd.

Cheers ...