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c++stringstreamscientific-notation

How to stop doubles converting to scientific notation when using a stringstream


I'm making a function to return the number of decimal and whole number digits and am converting the inserted typename number to a string using sstreams.

However the number when being converted to a string comes out in scientific notations which is not useful for counting the number of digits are in the normal number. How can I stop this from happening in my function below?

enum { DECIMALS = 10, WHOLE_NUMBS = 20, ALL = 30 };

template < typename T > int Numbs_Digits(T numb, int scope)
{
    stringstream ss(stringstream::in | stringstream::out);
    stringstream ss2(stringstream::in | stringstream::out);
    unsigned long int length = 0;
    unsigned long int numb_wholes;

    ss2 << (int) numb;
    numb_wholes = ss2.str().length();
    ss2.flush();
    bool all = false;

    switch (scope) {
    case ALL:
        all = true;

    case DECIMALS:
        ss << numb;
        length += ss.str().length() - (numb_wholes + 1);  // +1 for the "."
        if (all != true)
            break;

    case WHOLE_NUMBS:
        length += numb_wholes;
        if (all != true)
            break;

    default:
        break;
    }
    return length;
}

Solution

  • Use std::fixed stream manipulator as:

    ss << fixed << numb;
    

    --

    Example,

    #include <iostream>
    using namespace std;
    
    int main () {
      double a,b,c;
      a = 3.1415926534;
      b = 2006.0;
      c = 1.0e-10;
      cout.precision(5);
      cout       <<         a << '\t' << b << '\t' << c << endl;
      cout <<   fixed    << a << '\t' << b << '\t' << c << endl;
      cout << scientific << a << '\t' << b << '\t' << c << endl;
      return 0;
    }
    

    Output:

    3.1416          2006            1e-010
    3.14159         2006.00000      0.00000
    3.14159e+000    2.00600e+003    1.00000e-010
    

    Example is taken from here.

    And you can use std::stringstream instead of cout, but the result would be same. Experiment it here:

    http://www.ideone.com/HUrRw