One disadvantage of the macro-based approach - and it looks like greatest suffers from the same problem - which isn't actually that unusual - is the difficulty of setting a breakpoint on the code that fails a test. This comes in handy when a test fails and you'd like to investigate.

And due to C's limitations, you will actually have to do this quite often, on a wide range of failures, because the failure messages don't seem to print any details about the values being compared. So you'll need to hit the debugger to find out anything out.