iconv を使用した方法

std::string	SJIS_to_UTF8	(const std::string& sj_str)
{
	tstring	u8_str ;
	iconv_t	icd = ::iconv_open("UTF8","Shift_JIS") ;
	if (icd == (iconv_t)-1) {
		u8_str = ::iconv_SJIS_UTF8(sj_str) ;
		}
	else {
		{
			size_t	sj_size = sj_str.length() ;
			size_t	u8_size = sj_str.length()*3 + 1024 ;
			u8_str.resize(u8_size) ;
			char*	sj_ptr = (char*)(&sj_str[0]) ;
			char*	u8_ptr = (char*)(&u8_str[0]) ;
			::iconv(icd,&sj_ptr,&sj_size,&u8_ptr,&u8_size) ;
			}
		::iconv_close(icd) ;
		}
	return	u8_str.c_str() ;
	}

iconv，uconv の部分

#define	cmd_iconv		_T("iconv")		//	linux
#define	cmd_uconv		_T("uconv")		//	DS116
 
bool	exec_x_conv	(const tstring& s_j_name,const tstring& u_8_name)
{
	tstring	sj_name = ::QuotM_Add_Auto(s_j_name) ;
	tstring	u8_name = ::QuotM_Add_Auto(u_8_name) ;
	tstring	param = _T(" -f sjis -t utf8 ") + sj_name + _T(" -o ") + u8_name ;
	if (::which( cmd_iconv)) {
		tstring	 exe_iconv = cmd_iconv	_T(" ") + param ;
		_tsystem(exe_iconv.c_str()) ;
		return	true ;
		}
	if (::which( cmd_uconv)) {
		tstring	 exe_uconv = cmd_uconv	_T(" ") + param ;
		_tsystem(exe_uconv.c_str()) ;
		return	true ;
		}
	return	false ;
	}
 
std::string	iconv_SJIS_UTF8(const std::string& sj_str)
{
	tstring	tmp_path = ::Get_i_Tools_tmp_date() ;
	tstring	now_str  = ::Now_Format(_T("%M%S")) ;
	tstring	s_j_name = ::Path_AddLastSP(tmp_path) + _T("sj_") + now_str + _T(".txt") ;
	tstring	u_8_name = ::Path_AddLastSP(tmp_path) + _T("u8_") + now_str + _T(".txt") ;
		s_j_name = ::CreateUniqueEmpty(s_j_name.c_str()) ;
		u_8_name = ::CreateUniqueEmpty(u_8_name.c_str()) ;
	std::string	u8_str ;
	{
		v_char	v_c_u8 ;
		v_char	v_c_sj = ::To_v_char(sj_str.c_str()) ;
				 ::v_c_SaveText(s_j_name.c_str(),v_c_sj) ;
		{
				 ::exec_x_conv(s_j_name,u_8_name) ;
			}
		v_c_u8 = ::v_c_Load (u_8_name.c_str()) ;
		u8_str = ::To_tstring( v_c_u8   ).c_str() ;
		}
	return	u8_str.c_str() ;
	}

うまく置き換わっていない文字があった．
‘~'(0x7e) が ‘‾'(0x203e) になってしまっていた．
他にも ‘\'(0x5c) が ‘¥'(0xa5) ．
http://ossforum.jp/jossfiles/Linux_SJIS_Support.pdf
幾つか違う文字があるようで，iconv の -f sjis を SJIS-WIN でうまくいった．

	tstring	i_param = _T(" -f SJIS-WIN -t utf8 ") + sj_name + _T(" -o ") + u8_name ;
	tstring	u_param = _T(" -f sjis     -t utf8 ") + sj_name + _T(" -o ") + u8_name ;

2020/04/30　ASUSTOR NAS に対応
text_gnc.hxx exec_ic.hxx