The unary operator _Pragma, allows a preprocessor macro to be contained in a pragma directive.
_Pragma ( "pack(full)" )
#pragma pack(full)
In C++11, the _Pragma operator feature of the C99 preprocessor is adopted to provide a common preprocessor interface for C and C++ compilers. The _Pragma operator is an alternative method of specifying the #pragma directive. For more information, see C99 preprocessor features adopted in C++11 (C++11).