The unary operator _Pragma, allows a preprocessor macro to be contained in a pragma directive.
_Pragma ( "pack(full)" ) #pragma pack(full)
In C++0x,
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++0x (C++0x).