[ComputerGuru]

While MSVC doesn't have full C99 support, MSVC supported most of the features that shipped in C99 that make it much less painful to develop in C quite a number of years before C99 support formally landed in other compilers. MS will probably never support full C99 because the demand isn't there, but it's certainly not ANSI C you are expected to write.

[coldcat]

MSVC support C11 because it a prerequisite for C++17. The limits are you need to compile in C++, so the very few changes/incompatibilities between C and C++ always bend to the C++ choices. The preprocessor isn't what people used to have in C99 so some macro still not portable.

[ComputerGuru]

To the best of my knowledge (i.e. not updated since C++14), C++ is no longer a strict superset of C as of C99, and there are C99 features that are not available in C++, so I'm not sure that's the case. But plenty of overlap, for sure.

Here's a community wiki answer on SO: https://stackoverflow.com/posts/47526708/revisions

Extracted portion of relevance:

    > The following C99 features are not supported by C++:
    >
    > * restricted pointers
    > * variable length arrays
    > * flexible array members
    > * static and type qualifiers in parameter array declarators
    > * compound literals
    > * designated initializers