[Someone]

Yes, there is. Implementation defined means that a conforming implementation _must_ document its behavior.

That means that programmers don’t have to use trial and error to figure out how the compiler behaves and don’t have to _hope_ they found all the corner cases.

[berti]

And that is how we get #if defined(_THIS_THING_SOME_COMPILER_DEFINES) && !defined(__BUT_NOT_THIS_ONE_THAT_COMPILER_X_DEFINES) soup ;)

[greenhouse_gas]

Better than than silently ignoring an if guard preventing an overflow, and then overflowing anyways on addition.