Why do we need add these statements

Question

Hello,everybody, when I read the USES_CONVERSION macro, its definition like this:

 

#ifndef _DEBUG

#define USES_CONVERSION int _convert; (_convert); UINT _acp = ATL::_AtlGetConversionACP() /*CP_THREAD_ACP*/; (_acp); LPCWSTR _lpw; (_lpw); LPCSTR _lpa; (_lpa)

#else

#define USES_CONVERSION int _convert = 0; (_convert); UINT _acp = ATL::_AtlGetConversionACP() /*CP_THREAD_ACP*/; (_acp); LPCWSTR _lpw = NULL; (_lpw); LPCSTR _lpa = NULL; (_lpa)

#endif

 

It seems all 4 local variables have been declared, but after its declaration,there is another statement with parentheses enclosed,like (_convert). I am curious why we need such additional statement of the variable? and why this variable  was enclosed in parentheses? Does anyone have idea.

 

Answer 1

It avoids C4101, "unreferenced local variable" at warning level 4 if you never made a conversion.  Not sure about the parens.

Answer 2

Thank you, some reminding. it is helpful.