Fortran decimal and thousand separator

Question

Is there a way to change the period decimal separator for a comma?.

Also, how can I make the output numbers have a thousand separator?. This could be a comma, a period, a space ...

I actually asked a similar question: http://stackoverflow.com/a/21117594/2432130 — why.n0t, Aug 28 '14 at 11:55
@AlexanderVogt @Alex The difference is in the thousand separator, which is kind of tricky. POSIX locales know it, but C `printf` and `sprintf` ignore it. — Vladimir F Героям слава, Aug 28 '14 at 13:09
Ok, @Alex, so this: `write(*,'(dc,f12.3)') 12.3` sets the decimal separator I want. But still remains the thousand separator problem. — Antonio Serrano, Aug 29 '14 at 10:26

score 4 · Answer 1 · answered Aug 28 '14 at 10:46

4

Use the Argument DECIMAL='COMMA' when opening a file

open(100,file=logfile,status='unknown',DECIMAL='COMMA')

This will change the decimal to comma

answered Aug 28 '14 at 10:46

why.n0t

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2

Yes, but, what about if I want to print the numbers on the screen?. And what about the thousand separator?. – Antonio Serrano Aug 28 '14 at 11:08

score 4 · Answer 2 · edited May 23 '17 at 12:33

You can write a C++ function which will convert the number in a string in you current locale for you.

#include <string>
#include <iomanip> 
#include <sstream>

class SpaceSeparator: public std::numpunct<char>
{
public:
    SpaceSeparator(std::size_t refs): std::numpunct<char>(refs) {}
protected:
    char do_thousands_sep() const { return ' '; }
    char do_decimal_point() const { return ','; }
    std::string do_grouping() const { return "\03"; }
};

extern "C" {

void convert(char* str, double f, int len) {
  std::string s;
  std::stringstream out;
  SpaceSeparator facet(1); //1 - don't delete when done
  std::locale prev = out.imbue(std::locale(std::locale(), &facet));
  out << std::setprecision(15) << f;

  s = out.str();
  std::copy(s.begin(), s.end(), str);
  int i;
  for (i=s.size();i<len;i++){
    str[i] = ' ';
  }
}

}

call from Fortran:

  use iso_c_binding

  interface
    subroutine convert(str, f, l) bind(C,name="convert")
      import
      character(c_char) :: str(*)
      real(c_double), value :: f
      integer(c_int), value :: l
    end subroutine
  end interface

  character(len=100,kind=c_char) :: ch

  call convert(ch, 123456.123_c_double, len(ch, kind=c_int))
  print *,ch
end

On my machine it prints 123 456,123:

> gfortran locale.cc locale.f90 -lstdc++
> ./a.out 
 123 456,123

Disclaimer: I am not a C++ programmer and he solution can be slow. Maybe the brute force approach in Fortran is better.

I used this answer as a base: https://stackoverflow.com/a/2648663/721644

Thank you. But I think I will try a _more Fortran_ approach, programming my own function in Fortran to manage decimal and thousand separators. — Antonio Serrano, Aug 29 '14 at 09:53

score 2 · Answer 3 · edited Aug 28 '14 at 20:23

2

a quick and dirty fortran based approach:

  implicit none

  write(*,*) commadelim(123456.789)
  write(*,*) commadelim(23456.789)
  write(*,*) commadelim(3456.789)
  write(*,*) commadelim(-123456.789)
  write(*,*) commadelim(-23456.789)
  write(*,*) commadelim(-3456.789)

  contains

    function commadelim(v)
      implicit none

      real v
      integer dp,p,z0,i
      character(len=50) :: commadelim

      write(commadelim,'(f0.12)') abs(v)      
      dp = index(commadelim,'.')
      commadelim(dp:dp) = ','
      z0 = 2 - mod(dp+1,3)

      do i = 1, (dp+z0-1)/3-1
        p = 4*i-z0
        commadelim = commadelim(:p)//'.'//commadelim(p+1:)
      enddo

      if (v<0) commadelim = '-'//commadelim
    end function
  end

edited Aug 28 '14 at 20:23

Vladimir F Героям слава

57,977
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answered Aug 28 '14 at 17:04

agentp

6,849
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I really didn't understand this code, but I realize now that it deals with both thousand separators and the decimal separator. – Antonio Serrano Aug 29 '14 at 11:38
Which is more efficient, this code or the C++ code?. – Antonio Serrano Aug 29 '14 at 11:39
Efficiency has to be measured, but probably this one could be expected to be more efficient. It just manually forms the string from the number. It is straightforward Fortran, but for start you can just copy and paste the function. – Vladimir F Героям слава Aug 29 '14 at 12:24
how much data are you writing with thousands separators that efficiency is important? I like the self contained fortran for portability. OTOH it may take more work to ensure it is robust, plus you'll need to do some work to generalize to other format descriptors. – agentp Aug 29 '14 at 15:31
The code above has some errors, so it puts the comma in a wrong place and sometimes eliminates some digits. So, I will remake it and public it here. – Antonio Serrano Oct 27 '14 at 16:24

Fortran decimal and thousand separator

3 Answers3

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