August 2021
Intermediate to advanced
450 pages
6h 57m
Chinese
Content preview from C++程序设计语言（第4部分：标准库）（原书第4版）
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38.4 I/O操作
I/O操作的复杂性反映了习惯沿革、对I/O性能要求以及人们各种各样的需求。本节介绍的内容基于常规的英语小字符集（ASCII）。处理不同字符集和不同自然语言的方法将在第39章介绍。
38.4.1 输入操作
输入操作由istream提供，除了那些读取数据存入string的操作外，其他操作都定义在<istream>中。basic_istream主要作为更专用的输入类（如istream和istringstream）的基类：
对istream的用户而言，sentry类属于库的实现细节。它为标准库输入操作和用户自定义输入操作提供了公用代码。那些需要首先执行的代码（“前缀代码”）——例如刷新连接的流的代码——是以sentry的构造函数的方式提供的。例如：
sentry是供输入操作的实现者而非其用户使用的。
38.4.1.1 格式化输入
格式化输入功能主要由<<（“输入”、“获取”或“提取”）运算符提供：
istream（以及ostream）是“了解”内置类型的，因此x如果是一个内置类型，cin>>x意味着cin.operator>>（x）。如果x是一个用户自定义类型，cin>>x意味着operator>>（cin，x）（见18.2.5节）。即，iostream输入是类型敏感的、天生类型安全的且可扩展的。新类型的设计者可提供相应的I/O操作而无需直接访问iostream的实现。 ...
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