C# 将 20 位精度 double 转换为字符串并再次返回
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C# Converting 20 digit precision double to string and back again
提问by
In C#. I have a double (which I've extracted from a database) that has 20 digit precision. In Visual Studio (using QuickWatch) I can see the value of the double to be = 0.00034101243963859839.
在 C# 中。我有一个精度为 20 位的 double（我从数据库中提取的）。在 Visual Studio（使用 QuickWatch）中，我可以看到 double 的值为 = 0.00034101243963859839。
I want to display this value in a textbox and then have it be the same value when I take it out and convert it back into a double. But I always lose the last two digits
我想在文本框中显示这个值，然后在取出它并将其转换回双精度值时让它成为相同的值。但我总是输最后两位数
I've tried the following:
我尝试了以下方法：
double d = 0.00034101243963859839;
string s = d.ToString();
string s2 = d.ToString("F20");
string s3 = d.ToString("0.00000000000000000000"); -- 20 0's
string s4 = (d*100d).ToString();
In these cases:
在这些情况下：
s = 0.000341012439638598 s2 = 0.00034101243963859800 s3 = 0.00034101243963859800 s4 = 0.0341012439638598
I want to be able to do the following:
我希望能够做到以下几点：
double d = 0.00034101243963859839;
string s = d.ToString();
//...
double d2 = double.Parse(s);
if(d == d2)
{
//-- Success
}
Is there any way to keep those last two digits of precision??
有没有办法保持最后两位精度？
采纳答案by Joel Coehoorn
Use the "R" numeric format string:
使用“R”数字格式字符串：
double d = 0.00034101243963859839;
string s = d.ToString("R");
//...
double d2 = double.Parse(s);
if(d == d2)
{
//-- Success
}
The Rstands for "round-trip". From the linked document:
该R代表“往返”。从链接的文件：
This format is supported only for the Single and Double types. The round-trip specifier guarantees that a numeric value converted to a string will be parsed back into the same numeric value.
此格式仅支持 Single 和 Double 类型。往返说明符保证转换为字符串的数值将被解析回相同的数值。
As an aside, I suspect there is no way to keep those last two digits. There's only so much precision available, and I doubt they ever make it into din the first place. But you can make sure your string at least reads back what you do have correctly.
顺便说一句，我怀疑没有办法保留最后两位数字。可用的精度只有这么多，我怀疑他们一开始就没有做到d。但是您可以确保您的字符串至少可以正确读取您所做的内容。
If you really need the additional precision, you might try using a decimalinstead.
如果你真的需要额外的精度，你可以尝试使用 adecimal代替。
回答by Thorsten S.
No. Besides the fact that double is binary and therefore not good for decimal values, doubles have a maximum of 15/16 decimal digits (53 bits). decimal has a maximum of 28/29 digits (96 bit), so it would be ok to use it. If you have higher precisions in the database, you need an own bignum class for C#, look in stackoverflow for implementations.
不是。除了 double 是二进制的，因此不适用于十进制值这一事实之外，double 最多有 15/16 位十进制数字（53 位）。十进制最多有 28/29 位（96 位），所以可以使用它。如果你在数据库中有更高的精度，你需要一个自己的 C# bignum 类，在 stackoverflow 中查找实现。
