Created
April 12, 2012 07:10
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The solution to Linus' question on resolving undefined macros in the preprocessor to 0, as well as resolving defined macros to their values.
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| #include <stdio.h> | |
| #define CONFIG_FOO 1 | |
| #define CONFIG_NOO 0 | |
| #define is_set(macro) is_set_(macro) | |
| #define macrotest_1 , | |
| #define is_set_(value) is_set__(macrotest_##value) | |
| #define is_set__(comma) is_set___(comma 1, 0) | |
| #define is_set___(_, v, ...) v | |
| int main() | |
| { | |
| printf("It's %d!\n", is_set(FOO)); | |
| if(is_set(CONFIG_FOO)) | |
| { | |
| puts("And it's true, yo!"); | |
| } | |
| if(is_set(CONFIG_NOO)) | |
| { | |
| puts("Noooo!"); | |
| } | |
| if(is_set(CONFIG_NOTEXIST)) | |
| { | |
| puts("NOT EXIST"); | |
| } | |
| return 0; | |
| } |
An "#if is_set(CONFIG_FOO)" and "#if is_set(CONFIG_NOO)" work also as one might expect them to (true and false respectively).
can someone explain me how it works please?
@ProGNOmers: See torvalds/linux@69349c2 for an explanation.
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Just to complete it:
if is_set(CONFIG_FOO) == 1
printf("inside set option\n");
endif
if is_set(CONFIG_NOO) == 1
printf("inside unset option\n");
endif
if is_set(CONFIG_NOTEXIST) == 1
printf("inside non-existent option\n");
endif