hartmannathan commented on PR #15861:
URL: https://github.com/apache/nuttx/pull/15861#issuecomment-2698429383
> > Sure, won't argue, but #define BOARD_NGPIOINT 0 and no define at all is
the same thing. Preprocessor assigns 0 to the defines not given.
>
> @LuchianMihai I don't think that's true.
>
> ```
> $ cat main.c
> #include <stdio.h>
>
> #define MY_ZERO 0
>
> #ifdef MY_ZERO
> #warning "MY_ZERO is defined!"
> #else
> #warning "MY_ZERO is NOT defined!"
> #endif
>
> int main(int argc, const char * argv[])
> {
> printf("Hello, World!\n");
> return 0;
> }
>
> $ gcc main.c -o main
> main.c:6:2: warning: "MY_ZERO is defined!" [-W#warnings]
> #warning "MY_ZERO is defined!"
> ^
> 1 warning generated.
> ```
On further checking, I see what you mean:
```
$ cat main.c
#include <stdio.h>
#if (MY_ZERO == 0)
#warning "MY_ZERO is defined!"
#else
#warning "MY_ZERO is NOT defined!"
#endif
int main(int argc, const char * argv[])
{
printf("Hello, World!\n");
return 0;
}
$ gcc main.c -o main
main.cpp:4:2: warning: "MY_ZERO is defined!" [-W#warnings]
#warning "MY_ZERO is defined!"
^
1 warning generated.
```
So, for best safety, we need the condition to be written like this:
```
#include <stdio.h>
#if (defined MY_ZERO) && (MY_ZERO == 0)
#warning "MY_ZERO is defined!"
#else
#warning "MY_ZERO is NOT defined!"
#endif
int main(int argc, const char * argv[])
{
printf("Hello, World!\n");
return 0;
}
```
Then result is what we want:
```
$ gcc main.c -o main
main.cpp:6:2: warning: "MY_ZERO is NOT defined!" [-W#warnings]
#warning "MY_ZERO is NOT defined!"
^
1 warning generated.
```
So I learned something today! Thank you!
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