为什么按位移位(<< 和 >>)用于 cout 和 cin?

问题描述

问题确实在标题中；我敢肯定有一些合乎逻辑的，但现在我很难过！

Question is in the title really; I'm sure there is something logical, but for now I'm stumped!

推荐答案

根据C++的设计与演化的§8.3.1:

Doug McIlroy 通过类比 UNIX shell 中的 I/O 重定向操作符(>、>>、| 等)提出了提供输出操作符而不是命名输出函数的想法

The idea of providing an output operator rather than a named output function was suggested by Doug McIlroy by analogy with the I/O redirection operators in the UNIX shell (>, >>, |, etc.)

[...]

输入和输出操作考虑了几个操作符:赋值运算符是输入和输出的候选者，但它以错误的方式绑定.即 cout=a=b 将被解释为 cout=(a=b)，并且大多数人似乎更喜欢输入运算符与输出运算符不同.运算符<和>都试过了，但是小于"和大于"的含义已经牢牢地植入人们的脑海中，以至于新的I/O语句从所有实际目的来看都是不可读的(<<< 和 >>> 似乎不是这种情况).除此之外，'<'就在大多数键盘上的,"上方，人们写这样的表达方式:

Several operators were considered for input and output operations: the assignment operator was a candidate for both input and output, but it binds the wrong way. That is cout=a=b would be interpreted as cout=(a=b), and most people seemed to prefer the input operator to be different from the output operator. The operators < and > were tried, but the meanings "less than" and "greater than" were so firmly implanted in people's minds that the new I/O statements were for all practical purposes unreadable (this does not appear to be the case for << and >>). Apart from that, '<' is just above ',' on most keyboards, and people were writing expressions like this:

cout < x , y, z;

为此提供好的错误消息并不容易.

It is not easy to give good error messages for this.

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