How to clear width when outputting from a stream, after using std::setw?

Remember that the input operator >> stops reading at whitespace.

Use e.g. std::getline to get the remainder of the string:

std::stringstream ss("123ABCDEF1And then the rest of the string");
ss >> std::setw(3) >> nId
   >> std::setw(6) >> sLabel
   >> std::setw(1) >> bFlag;
std::getline(ss, sLeftovers);

std::setw only affects exactly one operation, i.e. >> bFlag will reset it to default, so you don't need to do anything to reset it.

i.e. your code should just work

std::stringstream ss("123ABCDEF1And then the rest of the string");
ss >> std::setw(3) >> nId
   >> std::setw(6) >> sLabel
   >> std::setw(1) >> bFlag
   >> sLeftovers;