格式说明符％一个在C的printf（） [英] The format specifier %a for printf() in C

问题描述

我读C语言的书，它说％F，％E，％G，％A 是用于浮printf的字符和双击数据类型。目前，我能理解％F，％E，％G 完全

I am reading a C language book, it said %f, %e, %g, %a were printf chars used for float and double data types. Currently I can understand %f, %e, %g completely.

当我需要用％A 打印浮动和双击类型的数据？

When do I need use %a to print float and double type data ?

能否请你告诉我一个例子。

Can you please show me an example.

推荐答案

的％A 格式化说明在C99是新的。它打印十六进制形式的浮点数。这是不是你会使用present号码的用户，但它是非常方便的在引擎罩/技术的使用案例。

The %a formatting specifier is new in C99. It prints the floating-point number in hexadecimal form. This is not something you would use to present numbers to users, but it's very handy for under-the-hood/technical use cases.

作为一个例子，这个code：

As an example, this code:

printf("pi=%a\n", 3.14);

打印：

pi=0x1.91eb86p+1

在评论中链接的优秀的文章解释说，这应该读1.91EB86 ₁₆ * 2 ¹ （也就是 p 是幂的两个浮点数字提高到的）。在这种情况下，1.91EB86 ₁₆ 是1.5700000524520874 ₁₀ 。乘以这个2 ¹ ，你会得到3.140000104904175 ₁₀

The excellent article linked in the comments explains that this should be read "1.91EB86₁₆ * 2¹" (that is, the p is for power-of-two the floating-point number is raised to). In this case, "1.91EB86₁₆" is "1.5700000524520874₁₀". Multiply this by the "2¹", and you get "3.140000104904175₁₀".

请注意，这也有preserving的有用的属性precision的所有位，和presenting他们在一个可靠的方法。

Note that this also has the useful property of preserving all bits of precision, and presenting them in a robust way.

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