c# - C# 如何*确切地*将 double 转换为十进制？

Question

以下 C# 代码打印 0.1 - 为什么？

var s = "0.1";
var dbl = Double.Parse(s);
var dcml = Convert.ToDecimal(dbl);
Console.WriteLine(dcml.ToString());

难道 0.01 不能用二进制表示，因此它应该打印 0.100000001490116 吗？

Answer 1

dbl 的值正好是 0.1000000000000000055511151231257827021181583404541015625。

这是 0.1 到 17 位有效数字。

documentation for Convert.ToDecimal(Double)状态:

The Decimal value returned by this method contains a maximum of 15 significant digits. If the value parameter contains more than 15 significant digits, it is rounded using rounding to nearest.

conversion from Single (aka float)被记录为更早截断:

The Decimal value returned by this method contains a maximum of seven significant digits. If the value parameter contains more than seven significant digits, it is rounded using rounding to nearest.

如果您调用 Convert.ToDecimal(Double) 并使用最初从 0.1f 转换而来的值，它将显示 0.100000001490116:

double dbl = 0.1f;        
decimal dcml = (decimal) dbl;
Console.WriteLine(dcml);