I'm interested in what purpose various platforms / compilers ("implementations") / frameworks assign to the the C and C++ preprocessor macro NDEBUG.
The C as well as the C++ standard only mention this definition once, namely to control the behavior of the assert() macro.
I would ask to include only specific answers, where you know that a certain platform / framework / library for C or C++ uses the NDEBUG definition to enable or disable anything else in addition to the standard defined assert() macro.
One reason for asking this question has been that MS (Visual-C++) always(?) uses "their" _DEBUG define to distinguish between debug and release stuff and I was wondering if this is a common practice for a library / platform to have their "own" debug define or whether other libraries / platforms use NDEBUGfor their debug related stuff.
That is a decision up to the maintainer(s) of the framework in question. Since such decisions are subject to change, it's nothing you should rely on. I use NDEBUG as a toggle for everything debug-related (e.g. trace outputs), but I might change my mind in the next release. No answer anyone could give here is a replacement for checking the API documentation of the frameworks you use in a given project.
That being said, using NDEBUG in library / framework headers, for anything else but assert(), would be a rather dumb design decision. The application programmer is explicitly allowed to set / unset NDEBUG however he sees fit, before and / or after including the headers of any library or framework, so the lib / framework maintainer could not rely on NDEBUG being set for a release lib or not set for a debugging lib. I doubt any significant project would have relied on NDEBUG that way.