C++ Standard Template Library (STL) 高级容器

最新推荐文章于 2025-09-12 18:45:12 发布

转载最新推荐文章于 2025-09-12 18:45:12 发布 · 68 阅读

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原文链接：http://www.cnblogs.com/greyqz/p/7691181.html

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#c/c++ #数据结构与算法

本文详细介绍了C++ STL中的map和set数据结构。包括定义、成员类型、常见操作如count()、find()等，并提供了使用示例。适用于初学者及需要深入理解这两种数据结构的开发者。

更多 STL 数据结构请阅读 NOIp 数据结构专题总结（STL structure 章节）

std::map

Definition:

template < class Key,                                     // map::key_type
           class T,                                       // map::mapped_type
           class Compare = less<Key>,                     // map::key_compare
           class Alloc = allocator<pair<const Key,T> >    // map::allocator_type
           > class map;

In a map, the key values are generally used to sort and uniquely identify the elements, while the mapped values store the content associated to this key. The types of key and mapped value may differ, and are grouped together in member type value_type, which is a pair type combining both:

typedef pair<const Key, T> value_type;

[WARNING] 如果不检查，直接返回 map[key]，可能会出现意想不到的行为。如果 map 包含 key，没有问题，如果 map 不包含 key，使用下标有一个危险的副作用，会在 map 中插入一个 key 的元素，value 取默认值，返回 value。也就是说，map[key] 不可能返回 null。

Functions:

count(): Count elements with a specific key

Searches the container for elements with a key equivalent to k and returns the number of matches.
Because all elements in a map container are unique, the function can only return 1 (if the element is found) or zero (otherwise).

find(): Get iterator to element (Recommend)

Searches the container for an element with a key equivalent to k and returns an iterator to it if found, otherwise it returns an iterator to map::end.

iter = m.find(key);
if (iter != m.end()) {
    return iter->second;
}
return null;

clear(): 清空 map

empty(): 判断是否为空返回 0，1

std::set

Definition:

template < class T,                        // set::key_type/value_type
           class Compare = less<T>,        // set::key_compare/value_compare
           class Alloc = allocator<T>      // set::allocator_type
           > class set;

In a set, the value of an element also identifies it (the value is itself the key, of type T), and each value must be unique. The value of the elements in a set cannot be modified once in the container (the elements are always const), but they can be inserted or removed from the container.