为什么C没有二进制文字? [英] Why doesn't C have binary literals?

问题描述

我经常希望我能在 c: 中做这样的事情:

I am frequently wishing I could do something like this in c:

val1 &= 0b00001111; //clear high nibble
val2 |= 0b01000000; //set bit 7
val3 &= ~0b00010000; //clear bit 5

拥有这种语法似乎是对 C 的一个非常有用的补充，没有我能想到的任何缺点，而且对于位旋转相当普遍的低级语言来说，这似乎是一件很自然的事情.

Having this syntax seems like an incredibly useful addition to C with no downsides that I can think of, and it seems like a natural thing for a low level language where bit-twiddling is fairly common.

我看到了其他一些很棒的选择，但是当有更复杂的面具时，它们都会崩溃.例如，如果 reg 是控制微控制器上 I/O 引脚的寄存器，我想同时将引脚 2、3 和 7 设置为高电平，我可以编写 reg =0x46; 但我不得不花 10 秒时间思考它(而且我可能不得不再花 10 秒时间再读一遍这些代码，因为一两天没看它)或者我可以写<代码>reg = (1 <<1) |(1 <<2) |(1 << 6); 但我个人认为这比写‘reg = 0b01000110;’要清楚得多我可以同意它不能很好地扩展到 8 位或 16 位架构之外.并不是说我需要制作 32 位掩码.

I'm seeing some other great alternatives but they all fall apart when there is a more complex mask. For example, if reg is a register that controls I/O pins on a microcontroller, and I want to set pins 2, 3, and 7 high at the same time I could write reg = 0x46; but I had to spend 10 seconds thinking about it (and I'll likely have to spend 10 seconds again every time I read those code after a not looking at it for a day or two) or I could write reg = (1 << 1) | (1 << 2) | (1 << 6); but personally I think that is way less clear than just writing `reg = 0b01000110;' I can agree that it doesn't scale well beyond 8 bit or maybe 16 bit architectures though. Not that I've ever needed to make a 32 bit mask.

推荐答案

根据国际标准的基本原理 - 编程语言 C §6.4.4.1 整数常量

According to Rationale for International Standard - Programming Languages C §6.4.4.1 Integer constants

由于缺乏先例和实用性不足，拒绝添加二进制常量的提议.

A proposal to add binary constants was rejected due to lack of precedent and insufficient utility.

它不在标准 C 中，但 GCC 支持它作为扩展，以 0b 或 0B 为前缀:

It's not in standard C, but GCC supports it as an extension, prefixed by 0b or 0B:

 i = 0b101010;

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