Is there a way to get an "undefined macro" warning with this code:
#if FOO \\do something #endif
but FOO is not defined?
@Per: Thanks, anyway I think that this approach should be avoided, see sourceware.org/.../Wundef
@Hans-Bernhard: thank you! It's a pity this options triggers a lot of other unneeded warnings that I'm not able to individually switch off.
Note that the link does not contain one sentence about the construct of using #error.
It all relates to a glibc policy and relating to the availability of the gcc-specific -Wundef
In a large number of situations, you aren't the owner of the original #define so you have no choice when it comes to #if xx or #if defined(xx) - you design based on what the library or target compiler supplies.
The main issue is to inform the developer that the code doesn't support, or hasn't been tested with, the current set of definitions.