为什么setw和width对于ostringstream不起作用？

Question

I have the following code:

template<typename _Tp>
std::string string_from_number(_Tp number, int precision = 5)
{
  std::ostringstream oss;
  oss.width(precision+1);
  oss<<number;
  return oss.str();
}

However the string length is not 5 as expected, but stays the default.
Replacing oss.width to oss<<std::setw does not work either. What am I doing wrong?

EDIT:

The problem appears clearly if the number is of double type say 0.123456789.

Answer 1

For controlling the number of digits displayed in a floating point number, the function you want is precision , not width . If you want to be sure you get the number displayed in fixed notation (rather than scientific) also look at the format flag fixed , used with the setf member function.