gcc-you can use this code to learn something about gcc, and inquire further into linux,
源代码在线查看： stdbool-if.c
/* { dg-do compile } */ /* { dg-options -pedantic } */ /* test of 'true' and 'false' in #if. this is accepted with a pedwarn before stdbool.h is included, silently afterward. */ /* Make sure they're viable keywords. */ bool a = true; bool b = false; #if true /* { dg-warning "true" "true in #if pedwarn" } */ #else #error true is false /* { dg-bogus "true" "true is false" } */ #endif #if false /* { dg-warning "false" "false in #if pedwarn" } */ #error false is true /* { dg-bogus "false" "false is true" } */ #endif #include /* Must still be viable keywords. */ bool c = true; bool d = false; #if true /* { dg-bogus "true" "true in #if with stdbool.h" } */ #else #error true is false /* { dg-bogus "true" "true is false" } */ #endif #if false /* { dg-bogus "false" "false in #if with stdbool.h" } */ #error false is true /* { dg-bogus "false" "false is true" } */ #endif
