双精度 [英] double and accuracy

问题描述

使用 long double 我得到 18/19 = 0.947368421052631578 ... 和 947368421052631578 是重复的十进制。使用 double 我得到 0.947368421052631526 ... 然而，前者是正确的。为什么会出现这样不正确的结果？

Using long double I get 18/19 = 0.947368421052631578..., and 947368421052631578 is the repeating decimal. Using double I get 0.947368421052631526... However, the former is correct. Why such an incorrect result?

感谢您的帮助。

推荐答案

A double 通常提供16（±1）个十进制数字。您的示例显示：

A double typically provides 16(±1) decimal digits. Your example shows this:

     4   8  12  16
     v   v   v   v
0.947368421052631578 long double
0.947368421052631526 double

答案同意16位数字。这是应该预期的。另请注意，C标准中不能保证 long double 比 double 更精确。

The answers agree to 16 digits. This is what should be expected. Also note that there's no guarantee in the C Standard that a long double has more precision than a double.

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