如何使用指定的指数将双值格式化为E格式？

Question

假设我有两个数字,0.0001和0.00001.

当我尝试在C#中使用"e"表示法格式化它们时,我得到以下结果:

double val = 0.0001;
Console.Out.WriteLine(val.ToString("e")) //prints 1e-4

double val2 = 0.00001;
Console.Out.WriteLine(val2.ToString("e")) //prints 1e-5

但我想格式化0.0001和0.00001以显示相同的指数,如下所示:

0.0001-> 100e-6 0.00001-> 10e-6

我怎样才能做到这一点？

Answer 1

如果你想要这个结果:

    1.0      = 1.00
    0.1      = 0.10
    0.01     = 0.010
    0.001    = 1.00e-3
    0.0001   = 0.10e-3
    0.00001  = 0.010e-3
    0.000001 = 1.00e-6

使用此代码:

class Program
{
    /// <summary>
    /// Format a value using engineering notation.
    /// </summary>
    /// <example>
    ///     Format("S4",-12345678.9) = "-12.34e-6"
    ///     with 4 significant digits
    /// </example>
    /// <arg name="format">The format specifier</arg>
    /// <arg name="value">The value</arg>
    /// <returns>A string representing the value formatted according to the format specifier</returns>
    public static string Format(string format, double value)
    {
        if(format.StartsWith("S"))
        {
            string dg=format.Substring(1);
            int significant_digits;
            int.TryParse(dg, out significant_digits);
            if(significant_digits==0) significant_digits=4;
            int sign;
            double amt;
            int exponent;
            SplitEngineeringParts(value, out sign, out amt, out exponent);
            return ComposeEngrFormat(significant_digits, sign, amt, exponent);
        }
        else
        {
            return value.ToString(format);
        }
    }
    static void SplitEngineeringParts(double value,
                out int sign,
                out double new_value,
                out int exponent)
    {
        sign=Math.Sign(value);
        value=Math.Abs(value);
        if(value>0.0)
        {
            if(value>1.0)
            {
                exponent=(int)(Math.Floor(Math.Log10(value)/3.0)*3.0);
            }
            else
            {
                exponent=(int)(Math.Ceiling(Math.Log10(value)/3.0)*3.0);
            }
        }
        else
        {
            exponent=0;
        }
        new_value=value*Math.Pow(10.0, -exponent);
        if(new_value>=1e3)
        {
            new_value/=1e3;
            exponent+=3;
        }
        if(new_value<=1e-3&&new_value>0)
        {
            new_value*=1e3;
            exponent-=3;
        }
    }
    static string ComposeEngrFormat(int significant_digits, int sign, double v, int exponent)
    {
        int expsign=Math.Sign(exponent);
        exponent=Math.Abs(exponent);
        int digits=v>0?(int)Math.Log10(v)+1:0;
        int decimals=Math.Max(significant_digits-digits, 0);
        double round=Math.Pow(10, -decimals);
        digits=v>0?(int)Math.Log10(v+0.5*round)+1:0;
        decimals=Math.Max(significant_digits-digits, 0);
        string t;
        string f="0:F";
        if(exponent==0)
        {
            t=string.Format("{"+f+decimals+"}", sign*v);
        }
        else
        {
            t=string.Format("{"+f+decimals+"}e{1}", sign*v, expsign*exponent);
        }
        return t;
    }

    static void Main(string[] args)
    {
        Console.WriteLine("\t1.0      = {0}", Format("S3", 1.0));
        Console.WriteLine("\t0.1      = {0}", Format("S3", 0.1));
        Console.WriteLine("\t0.01     = {0}", Format("S3", 0.01));
        Console.WriteLine("\t0.001    = {0}", Format("S3", 0.001));
        Console.WriteLine("\t0.0001   = {0}", Format("S3", 0.0001));
        Console.WriteLine("\t0.00001  = {0}", Format("S3", 0.00001));
        Console.WriteLine("\t0.000001 = {0}", Format("S3", 0.000001));
    }
}