August 2021
Intermediate to advanced
450 pages
5h 35m
Chinese
Content preview from C++语言导学（原书第2版）
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3.3 模块（C++20）
使用#include是一种古老的、易出错的且代价相当高的程序模块化组织方式。如果你在101个编译单元中使用#include header.h，编译器将会处理header.h的文本101次。如果你在header2.h之前使用#include header1.h，则header1.h中的声明和宏可能影响header2.h中代码的含义。相反，如果你在header1.h之前使用#include header2.h，则header2.h可能影响header1.h中的代码。显然，这不是一种理想的方式，实际上，自1972年这种机制被引入C语言之后，它就一直是额外代价和错误的主要来源。
我们的最终目的是想找到一种在C++中表达物理模块的更好方法。语言特性module尚未纳入ISO C++标准，但已是ISO技术规范[ModulesTS]。已有C++实现提供了module特性，因此我在这里冒一点风险推荐这个特性，虽然其细节可能发生改变，而且距离每个人都能使用它编写代码还有些时日。旧代码，即使用#include的代码，还会“生存”非常长的时间，因为代码更新代价很高且非常耗时。
我们考虑使用module表达3.2节中的Vector和use（）例子：
这段代码定义了一个名为Vector的模块，它导出类Vector及其所有成员函数和非成员函数size（）。
我们使用这个module的方式是在需要它的地方导入（import）它。例如：
我本可以对标准库数学函数也采用import，但我使用了老式的#include，借此展示新旧风格是可以混合的。在渐进地将#include旧代码更新为import新式代码的过程中，这种混合方式是必要的。 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.