April 2018
Intermediate to advanced
303 pages
4h 54m
Chinese
Content preview from Effective Modern C++（中文版）
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微调
｜
273
要点速记
•
对于可复制的、在移动成本低廉的并且一定会被复制的形参而言，按值传
递可能会和按引用传递的具备相近的效率，并可能生成更少量的目标代码。
•
经由构造复制形参的成本可能比经由赋值复制形参高出很多。
•
按值传递肯定会导致切片问题，所以基类型别特别不适用于按值传递。
条款
42
：考虑置入而非插入
如果你有个容器，持有一些，比如说，
std::string
型别的对象吧，那么似乎合
乎逻辑的做法是经由某个插入函数（
insertion function
）来向其添加新元素（比如
insert
、
push_front
和
push_back
，又或者对于
std::forward_list
而言的
insert_
after
），而你传递给函数的元素型别将是
std::string
。毕竟，那正是容器持有之物
的型别。
说合乎逻辑倒也确实合乎逻辑，但却不一定合乎事实。考虑这段代码：
std::vector<std::string> vs;
//
持有
std::string
型别对象的容器
vs.push_back(
"xyzzy"
);
//
添加字符串字面量
这里，容器持有的乃是
std::string
型别对象，但是你手头上有的（你实际上想要实
施
push_back
的）是个字符串字面量，即，一对引号内的一串字符。字符串字面量不
是
std::string
，也就是说，传递给
push_back
的实参并非容器持有之物的型别。
std::vector
的
push_back
针对左值
和右值给出了不同的重载版本如下：
template <class ...
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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.