gcc/testsuite/gcc.dg/cpp/20000207-2.c

/* { dg-do preprocess } */

/* Test for proper handling of unary plus in #if.  */

#if !(+1)
#error Error	/* { dg-bogus "Error" "case !(+1)" } */
#endif

#if !+1
#error Error	/* { dg-bogus "Error" "case !+1" } */
#endif

#if +1
#else
#error Error	/* { dg-bogus "Error" "case +1" } */
#endif