为什么以0x pfixed十六进制数$ P $？ [英] Why are hexadecimal numbers prefixed with 0x?

问题描述

为什么十六进制数prefixed为 0X ？
 据我所知，preFIX的用法，但我不明白为什么被选为 0X 的意义。

Why are hexadecimal numbers prefixed as 0x? I understand the usage of the prefix but I don't understand the significance of why 0x was chosen.

推荐答案

简单地说：的 0 告诉它在处理一个恒定的解析器（而不是一个标识符/保留字）。仍然需要一些东西来指定基数：在 X 是一个任意的选择

Short story: The 0 tells the parser it's dealing with a constant (and not an identifier/reserved word). Something is still needed to specify the number base: the x is an arbitrary choice.

龙的故事：在60年代，prevalent编程数字系统是十进制和的八的 - 大型机有每字节12，24或36位，这是3 =很好LOG2整除（8）。

Long story: In the 60's, the prevalent programming number systems were decimal and octal — mainframes had 12, 24 or 36 bits per byte, which is nicely divisible by 3 = log2(8).

在BCPL语言中使用的语法 8 1234 为八进制数字。当肯·汤普逊从BCPL创建B，他使用了 0 preFIX代替。这是伟大的，因为

The BCPL language used the syntax 8 1234 for octal numbers. When Ken Thompson created B from BCPL, he used the 0 prefix instead. This is great because

1. 整型常量现在总是由一个单一的令牌，


2. 解析器仍然可以告诉马上它有一个恒定的，


3. 解析器可以立即告诉底座（ 0 是在这两个基地是相同的），


4. 这是数学理智（ 00005 == 05 ）和


5. 没有precious（在＃123 的）。
需要特殊字符

1. an integer constant now always consists of a single token,
2. the parser can still tell right away it's got a constant,
3. the parser can immediately tell the base (0 is the same in both bases),
4. it's mathematically sane (00005 == 05), and
5. no precious special characters are needed (as in #123).

当下选自B创建，需要十六进制数出现（在PDP-11有16位字）及以上的所有的点仍然有效。由于八进制仍然需要其他机器， 0X 中任意选择（ 00 可能是排除了别扭）。

When C was created from B, the need for hexadecimal numbers arose (the PDP-11 had 16-bit words) and all of the points above were still valid. Since octals were still needed for other machines, 0x was arbitrarily chosen (00 was probably ruled out as awkward).

C＃是C的后代，所以它继承了语法。

C# is a descendant of C, so it inherits the syntax.

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