如何圆形双值，但保留尾随零 [英] How to round double values but keep trailing zeros

问题描述

在C＃我要舍入一个给定的双至小数点后一定量的函数。我总是希望我的功能与小数的一定量返回值（可以是一个字符串）。

In C# I want a function that rounds a given double to a given amount of decimals. I always want my function to return a value (which can be a string) with the given amount of decimals. If necessary, trailing zeros need to be added.

Example:

例>字符串结果= MyRoundingFunction（1.01234567，3）;
//这必须返回1.012

string result = MyRoundingFunction(1.01234567, 3); // this must return "1.012"

这很简单，它只是四舍五入并转换到串。但这里谈到的问题：

That's easy, it's just rounding and converting to string. But here comes the problem:

string result2 = MyRoundingFuntion(1.01, 3);
// this must return "1.010"

有没有做一个方便/标准方法这一点，或者我需要手动添加尾随零？

Is there a convenient/standard way to do this, or do I manually need to add trailing zeros?

任何帮助表示赞赏。需要注意的是在现实生活中的应用我不能硬编码的小数位数。

Any help is appreciated. Note that in the real life application I can't hard code the number of decimals.

推荐答案

您可以创建一个这样的例子格式化：

You can create a formatter like this example:

int numDigitsAfterPoint = 5;
double num = 1.25d;
string result = num.ToString("0." + new string('0', numDigitsAfterPoint));

或（更容易）

string result = num.ToString("F" + numDigitsAfterPoint);

一点题外话，的ToString 使用 MidpointRounding.AwayFromZero 而不是 MidpointRounding.ToEven （也称为银行家四舍五入）。作为一个例子：

As a sidenote, ToString uses the MidpointRounding.AwayFromZero instead of the MidpointRounding.ToEven (also called Banker's Rounding). As an example:

var x1 = 1.25.ToString("F1");
var x2 = 1.35.ToString("F1");
var x3 = Math.Round(1.25, 1).ToString();
var x4 = Math.Round(1.35, 1).ToString();

这会产生不同的结果（因为 Math.Round 通常使用 MidpointRounding.ToEven ）

These will produce different result (because Math.Round normally uses MidpointRounding.ToEven)

和注意，内部的ToString（）似乎舍入位之前做一些神奇。对于双打，如果你问他不到15位，我认为它四舍五入到前15位数字，然后舍入到的数字权数。看到这里 https://ideone.com/ZBEis9

And note that internally ToString() seems to do some "magic" before rounding digits. For doubles, if you ask him less than 15 digits, I think it rounds to 15 digits first and then rounds to the right number of digits. See here https://ideone.com/ZBEis9

这篇关于如何圆形双值，但保留尾随零的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！