How to format floating point value with fix number of digits?

Question

Is it possible in C# to format a double value with double.ToString in a way that I have always a fixed number of digits, no matter on which side of the decimal point?

Sa

Answer 1

I think some of your examples are wrong. But I still think that I understand what you want to achieve.

I made an extension method.

public static class StringExtensionMethods
{
    public static string ToString(this double d, int numberOfDigits)
    {
        var result = "";

        // Split the number.
        // Delimiter can vary depending on locale, should consider this and not use "."
        string[] split = d.ToString().Split(new string[] { "." }, StringSplitOptions.None);
        if(split[0].Count() >= numberOfDigits)
        {
            result = split[0].Substring(0, numberOfDigits);
        }
        else
        {
            result = split[0];
            result += ".";
            result += split[1];

            // Add padding.
            while(result.Count() < numberOfDigits +1)
                result += "0";

            result = result.Substring(0, numberOfDigits + 1);
        }

        return result;
    }
}

I ran it with your examples:

        double d0 = 0.00123456789;
        double d1 = 1.23456789;
        double d2 = 123.456789;
        double d3 = 0.0000000123456789;
        double d4 = 12345678.9;
        double d5 = 4.2;

        Console.WriteLine(d0.ToString(6));
        Console.WriteLine(d1.ToString(6));
        Console.WriteLine(d2.ToString(6));
        Console.WriteLine(d3.ToString(6));
        Console.WriteLine(d4.ToString(6));
        Console.WriteLine(d5.ToString(6));

This is the output:

0.00123 1.23456 123.456 1.23456 123456 4.20000

I don't think this is the best way to solve it, but I like extension methods.

DoubleConverter class: http://1drv.ms/1yEbvL4