Swap between at() and operator[] for std::vector depending on compile switch/NDEBUG

Question

I know that g++ (and MSVC) have switches that allow bounds checking on operator[] , unfortunately, to my knowledge, LLVM's libc++ doesn't have a complete implementation of such switches or debug code.

On my current project I have been using my own implementation of vector (that I wrote for portability a few years back) which doesn't throw exceptions and has assert based bounds checking on operator[] and at (in fact one calls the other and they behave identically as there are no exceptions).

I'm going to be handing over this code-base after I've finished my current program and it may be in use for a long time. Since I'm not supposed to be required to maintain it or anything I would rather be fully standard compliant everywhere and I don't feel that re-implementing a container is in the spirit of the standard, (I also highly doubt that my container is as good as one written by the libc++ or libstdc++ team).

Is there some preprocessor magic or similar that I can do to make operator[] behave like at() during debug (so it aborts due to an uncaught exception) and behave like operator[] when I disable this debug mode? (Project is fully C++14 supported)

Answer 1

We can see from the trunk libc++ source code for vector that there is indeed such a check inside std::vector<>::operator[], which goes through _LIBCPP_ASSERT.

Unfortunately, the libc++ debug feature is not yet functional.

So:

• Watch for libc++ updates
• Train your team to expect operator[] to silently accept broken input. That's what it does, by definition. Coming to rely on implementation-specific additional sanity checks is a really bad idea. Your team should be writing their own asserts if they're not sure what they're doing.