Question

I’m trying to convert an object with the value 0.39999999999999997 to a decimal variable without losing the precision.

object d = 0.39999999999999997;

I’ve tried the following methods.

decimal val1 = Convert.ToDecimal(d); // val1 = 0.4
object val2 = Convert.ChangeType(d, Type.GetType("System.Decimal")); // val2 = 0.4
decimal val3 = decimal.Parse(d.ToString()); // val3 = 0.4
decimal val4 = (Decimal) d; // val4 = 0.4

I know the this is not a problem with the decimal data type not being able to store this value as illustrated below.

decimal val5 = 0.39999999999999997m; // val5 = 0.39999999999999997;

How do I convert this object to decimal without losing the precision?

I’m using .NET Framework 3.5 if that matters.

Answer 1

I think this is the code you looking for:

object d = 0.39999999999999997;
//Unbox value
double doubleVal = (double)d;

//Convert to string. R format specifier gives a string that can round-trip to an identical number.  
//Without R ToString() result would be doubleAsString = "0.4"
string doubleAsString = doubleVal.ToString("R"); 

//Now that you have doubleAsString = "0.39999999999999997" parse it!
decimal decimalVal = decimal.Parse(doubleAsString);