在 C# 中实现复杂数字格式的最佳方法 [英] Best way to achieve complicated numeric formatting in C#

问题描述

在 C# 中复制此类行为的最佳方法是什么?

What is the best way to replicate the behaviour of something like this in C#?

// Converts decimal to a 0-padded string with minimum specified width and precision.
sprintf(out, "%0*.*lf", width, precision, decimal);

我阅读了标准、自定义 和 composite 格式字符串，但我看不出有什么好的方法可以实现这一点.

I had a read of standard, custom and composite format strings, but I can't see any nice way to achieve this.

我问的原因是我刚刚在我维护的一些代码中遇到了这个丑陋的片段，我们需要根据外部接口指定的可变宽度和精度来格式化一堆小数:

The reason I ask is that I just came across this ugly snippet in some code I am maintaining where we are required to format a bunch of decimals according to variable widths and precisions as specified by an external interface:

private static String ZEROS = "00000000000000000000000000";

public override string Format(decimal input, int width, int precision)
{
    String formatString = ZEROS.Substring(0, width - precision - 1) 
                          + "." + ZEROS.Substring(0, precision);
    return ToDecimal(input).ToString(formatString);
}

我想用一些不那么可怕的东西来代替它.

and I would like to replace it with someing a little less horrendous.

更新

由于最终答案隐藏在评论中，所以这里是:

Since the final answer is buried in comments, here it is:

public override string Format(decimal input, int width, int precision)
{
    string.Format("{0," + width + ":F" + precision + "}", input).Replace(" ","0");
}

在我的情况下，输入总是正的，所以这也有效:

In my case the input is always positive so this works too:

public override string Format(decimal input, int width, int precision)
{
    return input.ToString("F"+precision).PadLeft(width, 0);
}

推荐答案

你可以这样写，生成一个标准格式的字符串然后使用它:

You could write it like this, generating a standard format string and then using it:

public static string Format(decimal input, int width, int precision)
{
    var format = string.Format("{{0,{0}:F{1}}}", width, precision);
    // generates (e.g. width=15, precision=5)  "{0,15:F5}"
    // then format using this and replace padding with zeroes
    return string.Format(format, input).Replace(" ", "0");
}

或者不是两次调用 format 而是连接格式字符串，这取决于您的偏好:

Or instead of calling format twice just concat the format string, depending on your preference:

string.Format("{0," + width + ":F" + precision + "}", input).Replace(" ","0")

之后您必须替换空格，因为无法指定填充字符.或者，您可以编写自己的格式化程序来填充特定字符.这虽然有效:)

You have to replace the spaces afterwards since there's no way to specify the padding character. Alternately you could write your own formatter to pad with a specific character. This works though :)

这与所有输入的原始匹配，precision = 0 除外.在这种情况下，原始数据是不正确的，因为即使小数点不存在，它也会将小数点计为宽度的一部分.

This matches the original for all inputs except when precision = 0. In that case, the original is incorrect, since it counts the decimal point as part of the width even when it isn't present.

糟糕:忘记检查负数.

这是一个更简单的版本，但必须检查数字是否为负数才能使填充正确:

Here is a simpler version, but have to check if the number is negative to get the padding correct:

public override string Format(decimal input, int width, int precision)
{
    var output = input.ToString("F" + precision);
    return input < 0
        ? "-" + output.Substring(1).PadLeft(width, '0')
        :       output             .PadLeft(width, '0');
}

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