C99 introduced the _Pragma operator. This feature addresses a major problem with ‘#pragma’: being a directive, it cannot be produced as the result of macro expansion. _Pragma is an operator, much like sizeof or defined, and can be embedded in a macro.
Consider the following MWE, which will produce multiple errors, as the pragmas will be seemingly re-preprocessed.
#define CF_ASSUME_NONNULL_BEGIN _Pragma("clang assume_nonnull begin")
#define CF_ASSUME_NONNULL_END _Pragma("clang assume_nonnull end")
CF_ASSUME_NONNULL_BEGIN // error: already inside '#pragma clang assume_nonnull'
int bar = 42;
CF_ASSUME_NONNULL_END // error: not currently inside '#pragma clang assume_nonnull'
PPMacroCallback::MacroExpandsdeliberately omits expanding#pragmastatements and other preprocessor directives:https://github.com/Ericsson/CodeCompass/blob/d2b0ee675d01456658c7dd710661562022fc0398/plugins/cpp/parser/src/ppmacrocallback.cpp#L73-L77
However, pragmas can also be defined with the
_Pragmaoperator, see reference:https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html
Consider the following MWE, which will produce multiple errors, as the pragmas will be seemingly re-preprocessed.