ncurses demos: compile error with ncurses 6.0.20150808 GCC 6.3

[GitMensch]

Built under MinGW with make INFOEX=N CC="gcc $(ncursesw6-config --cflags)" LIBCURSES="$(ncursesw6-config --libs) -lpanelw" -k (something we may add to ncurses/README.md)

gcc -D_XOPEN_SOURCE=500 -I/mingw/include/ncursesw -I/mingw/include -Wall -Wextra -Werror -pedantic -O3 -D_XOPEN_SOURCE_EXTENDED -ombrot ../demos/mbrot.c -L/mingw/lib -lncursesw -lpsapi
../demos/mbrot.c: In function 'show_mandelbrot':
../demos/mbrot.c:111:27: error: implicit declaration of function 'alloc_pair' [-Werror=implicit-function-declaration]
                 int idx = alloc_pair( bot_rgb, top_rgb);
                           ^~~~~~~~~~
../demos/mbrot.c: In function 'main':
../demos/mbrot.c:248:13: error: implicit declaration of function 'init_extended_color' [-Werror=implicit-function-declaration]
             init_extended_color( i + COLOR0, red * 35 / 9, grn * 35 / 9, blu * 35 / 9);
             ^~~~~~~~~~~~~~~~~~~
../demos/mbrot.c:342:16: error: implicit declaration of function 'reset_color_pairs' [-Werror=implicit-function-declaration]
                reset_color_pairs( );
                ^~~~~~~~~~~~~~~~~
cc1.exe: all warnings being treated as errors
make: *** [mbrot] Error 1

gcc -D_XOPEN_SOURCE=500 -I/mingw/include/ncursesw -I/mingw/include -Wall -Wextra -Werror -pedantic -O3 -D_XOPEN_SOURCE_EXTENDED -otestcurs ../demos/testcurs.c -L/mingw/lib -lncursesw -lpsapi
../demos/testcurs.c: In function 'main':
../demos/testcurs.c:232:29: error: implicit declaration of function 'curses_trace' [-Werror=implicit-function-declaration]
                             curses_trace( flags);
                             ^~~~~~~~~~~~
In file included from ../demos/testcurs.c:33:0:
../demos/testcurs.c: In function 'attrTest':
d:/dev/MinGW/include/ncursesw/curses.h:1301:13: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
 #define wattr_set(win,a,p,opts)  (((win) \
                                  ~~~~~~~~~
        ? ((win)->_attrs = ((a) & ~A_COLOR), \
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           (win)->_color = (p)) \
           ~~~~~~~~~~~~~~~~~~~~~~
        : OK), \
        ~~~~~^~~
       OK)
       ~~~
d:/dev/MinGW/include/ncursesw/curses.h:1206:26: note: in expansion of macro 'wattr_set'
 #define attr_set(a,c,o)  wattr_set(stdscr,(a),(c),(o))
                          ^~~~~~~~~
../demos/testcurs.c:1558:5: note: in expansion of macro 'attr_set'
     attr_set( WA_TOP, 0, NULL);
     ^~~~~~~~
d:/dev/MinGW/include/ncursesw/curses.h:1301:13: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
 #define wattr_set(win,a,p,opts)  (((win) \
                                  ~~~~~~~~~
        ? ((win)->_attrs = ((a) & ~A_COLOR), \
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           (win)->_color = (p)) \
           ~~~~~~~~~~~~~~~~~~~~~~
        : OK), \
        ~~~~~^~~
       OK)
       ~~~
d:/dev/MinGW/include/ncursesw/curses.h:1206:26: note: in expansion of macro 'wattr_set'
 #define attr_set(a,c,o)  wattr_set(stdscr,(a),(c),(o))
                          ^~~~~~~~~
../demos/testcurs.c:1561:5: note: in expansion of macro 'attr_set'
     attr_set( WA_DIM, 0, NULL);
     ^~~~~~~~
d:/dev/MinGW/include/ncursesw/curses.h:1301:13: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
 #define wattr_set(win,a,p,opts)  (((win) \
                                  ~~~~~~~~~
        ? ((win)->_attrs = ((a) & ~A_COLOR), \
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           (win)->_color = (p)) \
           ~~~~~~~~~~~~~~~~~~~~~~
        : OK), \
        ~~~~~^~~
       OK)
       ~~~
d:/dev/MinGW/include/ncursesw/curses.h:1206:26: note: in expansion of macro 'wattr_set'
 #define attr_set(a,c,o)  wattr_set(stdscr,(a),(c),(o))
                          ^~~~~~~~~
../demos/testcurs.c:1565:5: note: in expansion of macro 'attr_set'
     attr_set( WA_ITALIC | WA_UNDERLINE, 0, NULL);
     ^~~~~~~~
d:/dev/MinGW/include/ncursesw/curses.h:1301:13: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
 #define wattr_set(win,a,p,opts)  (((win) \
                                  ~~~~~~~~~
        ? ((win)->_attrs = ((a) & ~A_COLOR), \
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           (win)->_color = (p)) \
           ~~~~~~~~~~~~~~~~~~~~~~
        : OK), \
        ~~~~~^~~
       OK)
       ~~~
d:/dev/MinGW/include/ncursesw/curses.h:1206:26: note: in expansion of macro 'wattr_set'
 #define attr_set(a,c,o)  wattr_set(stdscr,(a),(c),(o))
                          ^~~~~~~~~
../demos/testcurs.c:1575:5: note: in expansion of macro 'attr_set'
     attr_set( WA_LEFT, 0, NULL);
     ^~~~~~~~
d:/dev/MinGW/include/ncursesw/curses.h:1301:13: error: right-hand operand of comma expression has no effect [-Werror=unused-value]
 #define wattr_set(win,a,p,opts)  (((win) \
                                  ~~~~~~~~~
        ? ((win)->_attrs = ((a) & ~A_COLOR), \
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           (win)->_color = (p)) \
           ~~~~~~~~~~~~~~~~~~~~~~
        : OK), \
        ~~~~~^~~
       OK)
       ~~~
d:/dev/MinGW/include/ncursesw/curses.h:1206:26: note: in expansion of macro 'wattr_set'
 #define attr_set(a,c,o)  wattr_set(stdscr,(a),(c),(o))
                          ^~~~~~~~~
../demos/testcurs.c:1578:5: note: in expansion of macro 'attr_set'
     attr_set( WA_RIGHT, 0, NULL);
     ^~~~~~~~
cc1.exe: all warnings being treated as errors
make: *** [testcurs] Error 1

we may or may not be able to do something about those.

[Bill-Gray]

we may or may not be able to do something about those.

We can. ncurses provides a HAVE_ALLOC_PAIR #define; we'd need to do some logic along the lines of

#if HAVE_ALLOC_PAIR
(existing body of the Mandelbrot code)
#else
int main( const int argc, const char **argv)
{
    INTENTIONALLY_UNUSED_PARAMETER( argc);
    INTENTIONALLY_UNUSED_PARAMETER( argv);
   fprintf( stderr, "This demo requires the alloc_pair() function\n");
   return( 0);
}
#endif

For the testcurs.c case, we'd similarly make the call to curses_trace() dependent on HAVE_CURSES_TRACE.

Many of the ncurses demos use similar logic; there are a slew of HAVE_ macros that can be used to check that the library has the corresponding function...

...but we run into the problem that PDCurses* lacks those #defines, except in demos/ncurses_cfg.h, not included except by ncurses demos. I would argue that a heck of a lot of the #defines in question are unnecessary; if you don't, for example, HAVE_HALFDELAY or HAVE_GETWIN, do you really have curses at all?

But perhaps we should at least move HAVE_ALLOC_PAIR, and similar #defines used to show that a given function is available, out of demos/ncurses_cfg.h into curses.h... can't say I'd have any objection to that. The more I think it over, the more it makes sense to me.

[GitMensch]

Note: we can simply - at least for gcc and clang - also use --include ncurses.cfg.h when building from the ncurses folder, no need to change the files for that.
And yes, fixing the demos would be nice.

[Bill-Gray]

On a separate matter : I see I didn't write anything about the errors in testcurs.c springing from the use of the wattr_set() macro (at least, it's a macro in ncurses, sometimes, under somewhat unusual circumstances; "usually", it's a function). The problem appears to be that the macro returns the value OK, and then we ignore it.

I found some documentation stating that "to suppress the error[,] cast the unused expression to void." I wrote the following code to test the idea, roughly duplicating the 'logic' of the wattr_set() macro above :

#include <stdio.h>
#include <stdlib.h>

struct example
   {
   int a, b;
   };

#define example_macro( e, a, b, opts) (((e) \
           ? ((e)->a = ((a) & 0x7), \
              (e)->b = (b)) \
           : 42), \
           42)

int main( const int argc, const char **argv)
{
   if( 3 == argc)
      {
      const int a = atoi( argv[1]);
      const int b = atoi( argv[2]);
      struct example *ex = (struct example *)malloc( sizeof( struct example));

      (void)example_macro( ex, a, b, NULL);    /* NOTE CAST TO VOID */
      printf( "%d %d\n", ex->a, ex->b);
      if( ex)
         free( ex);
      }
   return( 0);
}

And indeed, including the (void) bit eliminated the warning. Omit (void), and you get the same sort of compiler warning/error that you got with testcurs.c.

So I suggest putting (void) in front of each call to attr_set(). (There are five of them, all in testcurs.c.) That should solve the problem. This is quite similar to the trick used in our INTENTIONALLY_UNUSED_PARAMETER macro.

[GitMensch]

Sounds good (maybe have a quick check that he compiler does not optimize the setting of "b" away in -O3).
I can give it a try once you do a fix commit.