问题描述
有两种方法可以轻松地创建一个键,C ++ STL中的值归属:映射和对的集合。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> >
在算法复杂性和编码风格方面,这些用法之间有什么区别?
In terms of algorithm complexity and coding style, what are the differences between these usages?
推荐答案
设置元素在集合中时无法修改。 set
的迭代器
和 const_iterator
是等效的。因此,用 set< pair< key_class,value_class> >
,您不能原地修改 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,这不会阻止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>
,您可以修改 value_class
参考地图。
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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