gcc/testsuite/gcc.dg/cpp/undef2.c

   1 /* C99 6.10.8 para 4: None of [the predefined macro names] shall be
   2    the subject of a #define or an #undef preprocessing directive.  */
   3
   4 /* { dg-do preprocess } */
   5
   6 #undef __DATE__         /* { dg-warning "undefining" "__DATE__" } */
   7 #undef __TIME__         /* { dg-warning "undefining" "__TIME__" } */
   8 #undef __FILE__         /* { dg-warning "undefining" "__FILE__" } */
   9 #undef __LINE__         /* { dg-warning "undefining" "__LINE__" } */
  10 #undef __STDC__         /* { dg-warning "undefining" "__STDC__" } */
  11
  12 /* These should be protected from #undef, but aren't, because they
  13    are set with normal #define commands - and on top of that, some
  14    of them are library properties, outside our control.  To consider:
  15    warn about undefining/redefining any identifier beginning with
  16    __STDC_ .
  17
  18    __STDC_HOSTED__
  19    __STDC_VERSION__
  20    __STDC_IEC_559__
  21    __STDC_IEC_559_COMPLEX__
  22    __STDC_ISO_10646__
  23  */