Generate all binary strings of length n with k bits set

Generate all binary strings of length n with k bits set.cpp

vector<string> answer;

void getStrings( string s, int digitsLeft )
{
   if( digitsLeft == 0 ) // the length of string is n
      answer.push_back( s );
   else
   {
      getStrings( s + "0", digitsLeft - 1 );
      getStrings( s + "1", digitsLeft - 1 );
   }
}

getStrings( "", n ); // initial call