Compiler Warning (level 4) C4233
For the latest documentation on Visual Studio 2017, see Visual Studio 2017 Documentation.
nonstandard extension used : 'keyword' keyword only supported in C++, not C
The compiler compiled your source code as C rather than C++, and you used a keyword that is only valid in C++. The compiler compiles your source file as C if the extension of the source file is .c or you use /Tc.
This warning is automatically promoted to an error. If you wish to modify this behavior, use #pragma warning. For example, to make C4233 into a level 4 warning issue,
in your source code file.