background preloader

Std::map

Facebook Twitter

Map (C++) Design[edit] Characteristics[edit] Key uniqueness: in map and set each key must be unique. multimap and multiset do not have this restriction.Element composition: in map and multimap each element is composed from a key and a mapped value. In set and multiset each element is key; there are no mapped values.Element ordering: elements follow a strict weak ordering[1] The associative containers can be grouped into two subsets: maps and sets. A map, sometimes referred to as a dictionary, consists of a key/value pair. Both map and set only allow one instance of a key or element to be inserted into the container. Both maps and sets support bidirectional iterators. While not officially part of the STL standard, hash_map and hash_set are commonly used to improve searching times. Performance[edit] The asymptotic complexity of the operations that can be applied to associative containers are as follows: Overview of functions[edit] Usage[edit] Iterators[edit] References[edit]

Loop through map and print all the key/value pair : map iterator « Map Multimap « C++ STL Tutorial - Map Class. Suppose that you're working with some data that has values associated with strings -- for instance, you might have student usernames and you want to assign them grades. How would you go about storing this in C++? One option would be to write your own hash table. This will require writing a hash function and handling collisions, and lots of testing to make sure you got it right. On the other hand, the standard template library (STL) includes a templated class to handle just this sort of situation: the STL map class, which conceptually you can think of as an "associative array" -- key names are associated with particular values (e.g., you might use a student name as a key, and the student's grade as the data).

In fact, the STL's map class allows you to store data by any type of key instead of simply by a numerical key, the way you must access an array or vector. To use the map class, you will need to include <map> and maps are part of the std namespace. Std::map <string, char> grade_list; Map. Maps are associative containers that store elements formed by a combination of a key value and a mapped value, following a specific order. 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: Internally, the elements in a map are always sorted by its key following a specific strict weak ordering criterion indicated by its internal comparison object (of type Compare). map containers are generally slower than unordered_map containers to access individual elements by their key, but they allow the direct iteration on subsets based on their order.

The mapped values in a map can be accessed directly by their corresponding key using the bracket operator ((operator[]). Maps are typically implemented as binary search trees.