digitalmars.D.learn - string to real conversion losing data

jicman (39/39) Apr 08 2010 Greetings and salutations!

wrzosk (8/47) Apr 08 2010 it is looking ok to me, try this one and thing why it is like that :)

jicman (4/17) Apr 08 2010 Ok, I'll bite... I don't get it. does that mean that writefln is buggy?...

bearophile (14/16) Apr 08 2010 This prints the same values, using latest D2:

BCS (10/11) Apr 08 2010 Never trust your output function :) (e.i. always check to see if it's do...

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (16/64) Apr 08 2010 The default format string for floating point values is 6 decimal digits

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (9/10) Apr 08 2010 Well... That will be too many digits unless the number of digits before
jicman (3/73) Apr 09 2010 thanks. That worked.

jicman <cabrera_ _wrc.xerox.com> writes:

Greetings and salutations!

Will someone be so kind as to explain why this is happening?

----
import std.stdio;
import std.conv;

void main()
{
  char[][] strRealVals =
  [
    "14539.34","1230.00","361.62","1613.10","","","0.00"
  ];
  real rTotal = 0;
  foreach (char[] s; strRealVals)
  {
    writefln("Real value is: " ~ s);
    real r = 0.00;
    if (s != "")
      r = std.conv.toReal(s);
    rTotal += r;
  }
  writefln(std.string.toString(rTotal));
  writefln(rTotal);
}
----

When I run this program, I get this:
16:51:35.54>realtest
Real value is: 14539.34
Real value is: 1230.00
Real value is: 361.62
Real value is: 1613.10
Real value is:
Real value is:
Real value is: 0.00
17744.1
17744.1

----

If I add these numbers, the outcome should be 17744.06.  Any ideas?  I am using
Digital Mars D Compiler v1.046.

thanks,

jos�

Apr 08 2010

wrzosk <dprogr gmail.com> writes:

W dniu 08.04.2010 23:02, jicman pisze:
 Greetings and salutations!

 Will someone be so kind as to explain why this is happening?

 ----
 import std.stdio;
 import std.conv;

 void main()
 {
    char[][] strRealVals =
    [
      "14539.34","1230.00","361.62","1613.10","","","0.00"
    ];
    real rTotal = 0;
    foreach (char[] s; strRealVals)
    {
      writefln("Real value is: " ~ s);
      real r = 0.00;
      if (s != "")
        r = std.conv.toReal(s);
      rTotal += r;
    }
    writefln(std.string.toString(rTotal));
    writefln(rTotal);
 }
 ----

 When I run this program, I get this:
 16:51:35.54>realtest
 Real value is: 14539.34
 Real value is: 1230.00
 Real value is: 361.62
 Real value is: 1613.10
 Real value is:
 Real value is:
 Real value is: 0.00
 17744.1
 17744.1

 ----

 If I add these numbers, the outcome should be 17744.06.  Any ideas?  I am
using Digital Mars D Compiler v1.046.

 thanks,

 jos�

it is looking ok to me, try this one and thing why it is like that :)


import std.stdio;
import std.conv;

void main()
{
	writefln(17744.06);
}

Apr 08 2010

jicman <cabrera_ _wrc.xerox.com> writes:

wrzosk Wrote:

 W dniu 08.04.2010 23:02, jicman pisze:

 
 it is looking ok to me, try this one and thing why it is like that :)
 
 
 import std.stdio;
 import std.conv;
 
 void main()
 {
 	writefln(17744.06);
 }

Ok, I'll bite... I don't get it.  does that mean that writefln is buggy?  How
can I format and write this to a file?  Is there a formatting library?

thanks,

jose

Apr 08 2010

bearophile <bearophileHUGS lycos.com> writes:

 If I add these numbers, the outcome should be 17744.06.  Any ideas?  I am
using Digital Mars D Compiler v1.046.
 jos�

This prints the same values, using latest D2:


import std.stdio, std.conv;

void main() {
    real tot = 0;
    foreach(el; ["14539.34","1230.00","361.62","1613.10","0.00"])
        tot += to!real(el);
    writefln("%.5f\n", tot); // 17744.06000

    tot = 0;
    foreach(el; [14539.34,1230.00,361.62,1613.10,0.00])
        tot += to!real(el);
    writefln("%.5f\n", tot); // 17744.06000
}

Bye,
bearophile

Apr 08 2010

BCS <none anon.com> writes:

Hello bearophile,

 writefln("%.5f\n", tot); // 17744.06000

Never trust your output function :) (e.i. always check to see if it's doing 
what you think it is.)

Back in the bad old days, a guy I knew spent a while debugging a problem 
that turned out to be that he was loading data as float but storing it into 
an int (think an invalid scanf format string). Every time he checked things 
though things seems OK because he had the same bug in his output as well 
(think printf).

-- 
... <IXOYE><

Apr 08 2010

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

jicman wrote:
 Greetings and salutations!
 
 Will someone be so kind as to explain why this is happening?
 
 ----
 import std.stdio;
 import std.conv;
 
 void main()
 {
   char[][] strRealVals =
   [
     "14539.34","1230.00","361.62","1613.10","","","0.00"
   ];
   real rTotal = 0;
   foreach (char[] s; strRealVals)
   {
     writefln("Real value is: " ~ s);
     real r = 0.00;
     if (s != "")
       r = std.conv.toReal(s);
     rTotal += r;
   }
   writefln(std.string.toString(rTotal));
   writefln(rTotal);
 }
 ----
 
 When I run this program, I get this:
 16:51:35.54>realtest
 Real value is: 14539.34
 Real value is: 1230.00
 Real value is: 361.62
 Real value is: 1613.10
 Real value is:
 Real value is:
 Real value is: 0.00
 17744.1
 17744.1
 
 ----
 
 If I add these numbers, the outcome should be 17744.06.  Any ideas?  I am
using Digital Mars D Compiler v1.046.
 
 thanks,
 
 jos�
 

The default format string for floating point values is 6 decimal digits 
of precision (the digits before and after the decimal point). writefln 
is rounding the value up.

Try for example "%.18f" for 'real'. This does it automatically:

import std.stdio;
import std.string;

void main()
{
     auto theValue = 17744.06L;

     writefln("%s has %s decimal digits of precision",
              typeof(theValue).stringof, theValue.dig);

     auto formatString = format("%%.%sf", theValue.dig);
     writefln(formatString, theValue);
}

Ali

Apr 08 2010

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

Ali Çehreli wrote:

 Try for example "%.18f" for 'real'.

Well... That will be too many digits unless the number of digits before 
the decimal point is zero.

The decimal digits before and after the point should be 18 for most 
accurate representation. But the OP probably doesn't need that many 
digits anyway.

Here are more options:

   http://digitalmars.com/d/2.0/phobos/std_format.html

Ali

Apr 08 2010

jicman <cabrera_ _wrc.xerox.com> writes:

Ali Çehreli Wrote:

 jicman wrote:
 Greetings and salutations!
 
 Will someone be so kind as to explain why this is happening?
 
 ----
 import std.stdio;
 import std.conv;
 
 void main()
 {
   char[][] strRealVals =
   [
     "14539.34","1230.00","361.62","1613.10","","","0.00"
   ];
   real rTotal = 0;
   foreach (char[] s; strRealVals)
   {
     writefln("Real value is: " ~ s);
     real r = 0.00;
     if (s != "")
       r = std.conv.toReal(s);
     rTotal += r;
   }
   writefln(std.string.toString(rTotal));
   writefln(rTotal);
 }
 ----
 
 When I run this program, I get this:
 16:51:35.54>realtest
 Real value is: 14539.34
 Real value is: 1230.00
 Real value is: 361.62
 Real value is: 1613.10
 Real value is:
 Real value is:
 Real value is: 0.00
 17744.1
 17744.1
 
 ----
 
 If I add these numbers, the outcome should be 17744.06.  Any ideas?  I am
using Digital Mars D Compiler v1.046.
 
 thanks,
 
 jos�
 

 
 The default format string for floating point values is 6 decimal digits 
 of precision (the digits before and after the decimal point). writefln 
 is rounding the value up.
 
 Try for example "%.18f" for 'real'. This does it automatically:
 
 import std.stdio;
 import std.string;
 
 void main()
 {
      auto theValue = 17744.06L;
 
      writefln("%s has %s decimal digits of precision",
               typeof(theValue).stringof, theValue.dig);
 
      auto formatString = format("%%.%sf", theValue.dig);
      writefln(formatString, theValue);
 }
 

thanks.  That worked.

jic

Apr 09 2010

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digitalmars.D.learn - string to real conversion losing data