Well it should be backwards compatible if you just use NULL everywhere where it is appropriate, so you wouldn't even have to sprinkle ifdefs all over the place.

Well it should be backwards compatible if you just use NULL everywhere where it is appropriate, so you wouldn't even have to sprinkle ifdefs all over the place. Code that uses 0 all over the place would probably have to be updated with the help of compiler errors and a static code analyzer.