C++ :: Splitting Directory Path Up - Function Call Missing Argument List

Code:
void CFileManager::SplitHeader(std::string sFilePath) {
std::string sDrive(255, ');
std::string sDirectory(255, ');
std::string sFileName(255, ');
std::string sExtension(255, ');

_splitpath_s(&sFilePath[0], &sDrive[0], sDrive.size, &sDirectory[0], sDirectory.size, &sFileName[0], sFileName.size, &sExtension[0], sExtension.size);
}

Which gives me error

Error 1 error C3867: 'std::basic_string<char,std::char_traits<char>,std ::allocator<char>>::size': function call missing argument list; use '&std::basic_string<char,std::char_traits<char>,st d::allocator<char>>::size' to create a pointer to member.