where the preprocessing token STDC does not immediately follow pragma in the directive (prior to any macro replacement) causes the implementation to behave in an implementation-defined manner. ...
Pragma directives are only part of the C standard if followed by STDC. The ISO C++ standard does not require any pragmas to be supported at all, though most compilers will support at least the ones required by C even in C++ mode.
A preprocessing directive of the form
where the preprocessing token STDC does not immediately follow pragma in the directive (prior to any macro replacement) causes the implementation to behave in an implementation-defined manner. ...Pragma directives are only part of the C standard if followed by STDC. The ISO C++ standard does not require any pragmas to be supported at all, though most compilers will support at least the ones required by C even in C++ mode.