> In your case, how much compatibility is lost from using C99 over C89?
Until somewhat recently C89 was the latest version of C that was supported by the MSVC compiler. Support for C99 was always terribly broken and Microsoft chose to claim it did supported C99 but without supporting mandatory features, which meant they did not in fact supported C99.
This sad state of affairs only changed significantly in 2020, with a lowkey announcement.
They claimed support for C99 to the extent required for ISO C++ compliance, plus some features critical for a couple of their developers.
Likewise, even with the updated C11 and C17 support, it isn't 100% there, only good enough, because C++ is what matters for Windows developers when not using .NET.
Until somewhat recently C89 was the latest version of C that was supported by the MSVC compiler. Support for C99 was always terribly broken and Microsoft chose to claim it did supported C99 but without supporting mandatory features, which meant they did not in fact supported C99.
This sad state of affairs only changed significantly in 2020, with a lowkey announcement.
https://devblogs.microsoft.com/cppblog/c11-and-c17-standard-...