Formatting doubles for output in C#

by

The problem is that .NET will always round a double to 15 significant decimal digits before applying your formatting, regardless of the precision requested by your format and regardless of the exact decimal value of the binary number.

I’d guess that the Visual Studio debugger has its own format/display routines that directly access the internal binary number, hence the discrepancies between your C# code, your C code and the debugger.

There’s nothing built-in that will allow you to access the exact decimal value of a double, or to enable you to format a double to a specific number of decimal places, but you could do this yourself by picking apart the internal binary number and rebuilding it as a string representation of the decimal value.

Alternatively, you could use Jon Skeet’s DoubleConverter class (linked to from his “Binary floating point and .NET” article). This has a ToExactString method which returns the exact decimal value of a double. You could easily modify this to enable rounding of the output to a specific precision.

double i = 10 * 0.69;
Console.WriteLine(DoubleConverter.ToExactString(i));
Console.WriteLine(DoubleConverter.ToExactString(6.9 - i));
Console.WriteLine(DoubleConverter.ToExactString(6.9));

// 6.89999999999999946709294817992486059665679931640625
// 0.00000000000000088817841970012523233890533447265625
// 6.9000000000000003552713678800500929355621337890625

More Related Contents:

  1. Is floating-point math consistent in C#? Can it be?
  2. Coercing floating-point to be deterministic in .NET?
  3. How to calculate float type precision and does it make sense?
  4. How to escape braces (curly brackets) in a format string in .NET
  5. Double to string conversion without scientific notation
  6. When should I use double instead of decimal?
  7. How can I String.Format a TimeSpan object with a custom format in .NET?
  8. How To Represent 0.1 In Floating Point Arithmetic And Decimal
  9. How to convert a Decimal to a Double in C#?
  10. What does {0} mean when found in a string in C#?
  11. Extracting mantissa and exponent from double in c#
  12. Compare floats in Unity
  13. Format Number like Stack Overflow (rounded to thousands with K suffix)
  14. How deterministic is floating point inaccuracy?
  15. Format A TimeSpan With Years
  16. Representing integers in doubles
  17. Convert from scientific notation string to float in C#
  18. How do I convert an array of floats to a byte[] and back?
  19. Format a number with commas and decimals in C# (asp.net MVC3)
  20. Two Decimal places using c#
  21. How to split string preserving whole words?
  22. Is it safe to assume floating point is represented using IEEE754 floats in C?
  23. Status of __STDC_IEC_559__ with modern C compilers
  24. How to convert Decimal to Double in C#?
  25. Uses for negative zero floating point value?
  26. File-size format provider
  27. Extra leading zeros when printing float using printf?
  28. What’s the best way to represent System.Decimal in Protocol Buffers?
  29. How to get floats value without including exponential notation
  30. Formatting Large Numbers with .NET

Leave a Comment