printf() 中的井号“#"有什么作用? [英] What does a hash sign '#' do in printf()?

问题描述

int x = 0xff;
printf("%#x",x);

输出:0xff

printf("%x",x);

输出:ff

为什么输出有差异?# 具体是做什么的?

Why is there a difference in output? What does # specifically do?

推荐答案

标准说:

7.21.6 - 2

结果被转换为替代形式".... 对于 x(或 X)转换，非零结果带有 0x(或 0X)前缀.

The result is converted to an ‘‘alternative form’’. ... For x (or X) conversion, a nonzero result has 0x (or 0X) prefixed to it.

它还有其他有趣的东西(尤其是花车)，但我很少看到它被使用——老实说，我不得不查阅它才能记住.

It does other interesting stuff (especially for floats) but I have rarely seen it used - I honestly admit I had to look it up to remember.

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