如何用固定位数格式化浮点值? [英] How to format floating point value with fix number of digits?

问题描述

在C#中是否可以用double.ToString格式化双精度值，而无论小数点的哪一边，我总是具有固定的数字位数?

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?

说我希望有6位数字，我想要这些结果:

Say I wish 6 digits, I want to have these results:

• 0.00123456789给出"0.00123"
• 1.23456789给出"1.23457"
• 123.456789给出"123.457"
• 0.0000000123456789给出"0.00000"
• 12345678.9给出"12345679"(发生溢出时，我想查看小数点后的所有数字)
• 4.2给出"4.20000"

我正在尝试使用double.ToString，但是找不到任何合适的格式字符串.

I'm experimenting with double.ToString, but cannot find any suitable format string.

已经尝试使用"G6"(有时会采用指数格式)，"F6"(即将关闭，但0.123456789会给出7位数的"0.123457").

Already tried "G6" (gives sometimes exponential format), "F6" (comes close, but 0.123456789 gives "0.123457" which are 7 digits).

推荐答案

我认为您的某些示例是错误的. 但是我仍然认为我了解您想要实现的目标.

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

我做了一个扩展方法.

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;
    }
}

我用您的示例来运行它:

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));

这是输出:

0.00123 1.23456 123.456 1.23456 123456 4.20000

0.00123 1.23456 123.456 1.23456 123456 4.20000

我认为这不是解决问题的最佳方法，但是我喜欢扩展方法.

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

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

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

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