set<pair> 和 set<pair> 有什么区别?并用 C++ 映射? [英] What's the difference between set<pair> and map in C++?

问题描述

有两种方法可以在 C++ STL 中轻松创建键值属性:映射和对集.例如，我可能有

There are two ways in which I can easily make a key,value attribution in C++ STL: maps and sets of pairs. For instance, I might have

map<key_class,value_class>

或

set<pair<key_class,value_class> >

在算法复杂度和编码风格方面，这些用法有什么区别?

In terms of algorithm complexity and coding style, what are the differences between these usages?

推荐答案

集合中的元素不能被修改.set 的 iterator 和 const_iterator 是等价的.因此，用 set;>，您不能就地修改 value_class.您必须从集合中删除旧值并添加新值.但是，如果 value_class 是一个指针，这并不妨碍您修改它指向的对象.

Set elements cannot be modified while they are in the set. set's iterator and const_iterator are equivalent. Therefore, with set<pair<key_class,value_class> >, you cannot modify the value_class in-place. You must remove the old value from the set and add the new value. However, if value_class is a pointer, this doesn't prevent you from modifying the object it points to.

使用 map<key_class,value_class>，您可以就地修改 value_class，假设您有一个对地图的非常量引用.

With map<key_class,value_class>, you can modify the value_class in-place, assuming you have a non-const reference to the map.

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