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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31.4 容器
本节继续深入讨论一些细节：
·vector及其构造函数（见31.4.1节）。
·链表：list和forward_list（见31.4.2节）。
·关联容器，如map和unordered_map（见31.4.3节）。
31.4.1 vector
STL的vector是默认容器——除非你有充分理由，否则应该使用它。如果你希望使用链表或内置数组替代vector，应慎重考虑后再做决定。
31.3节介绍了vector上的操作，并隐含地与其他容器上的操作进行了对比。但是，在了解了vector的重要性之后，本节继续深入讨论它，重点介绍其操作是如何实现的。
vector的模板参数和成员类型定义如下：
31.4.1.1 vector和增长
考虑一个vector对象的内存布局（如13.6节所述）：
使用大小（元素数目）和容量（不重新分配空间的前提下可容纳的元素数目）令push_back（）操作时的向量增长相当高效：不会在添加每个元素时都分配内存，而是在超出容量时才进行一次重新分配（见13.6节）。C++标准并未指定超出容量时向量的增长幅度，但很多C++实现都是增加大小的一半。曾经有一段时间，当读取输入存入一个vector时，我总是注意使用reserve（）。但我惊讶地发现，基本上所有情况下，调用reserve（）都不会带来可测量的性能变化。默认的增长策略与我自己预测分配做得一样好，因此我就停止使用reserve（）来提高性能了。取而代之，我用它来提高重分配延迟的可预测性以及避免指针和迭代器失效。 ...
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