Re: string to real conversion losing data

[Ali Çehreli]

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