STL-Associative Containers

Associative Containers Sequence containers : "This is item 0, this is item 1, this is item 2…“ Associative containers : – Store items by key: I have the word "apple" I have the word "carrot" – No numeric index – word[0] is meaningless

Sets Set – Stores set of items – One copy max of each value – Items stored according to < operator Can change

Set Demo

No indexes! No index access: Always need iterators:

Other Set Tools find(item) returns an iterator to item – Returns end() if not found erase() takes value or iterator

Multiset Same as Set, but duplicates allowed – Also in Set library

Grouping Things Complex groupings deserve struct/class – Class if has behaviors – Struct – simple data Do we really want lots of structs like  ?

Pair Pair template in library Looks like:

Pair Use Only has first/second Can "construct" with initializer list

Pair Use Can make a vector of pairs: But associations not explicitly stored – No order – No easy way to look up things

Map Stores a sorted list of key/value pairs Key A B C D E Value Apple Banana Carrot Dingo Elf

Map Key used as index into list – Assigning creates record Key A B C D E Value Apple Banana Carrot Dingo Elf

Map Gotcha Accessing a key adds it to the Map with default value

Ways to insert: Insertions – Map stores pairs, multiple ways to add:

Ways to insert: Each key can have only one value:

Iteration: Use iterators just like vector – Access parts with first/second Map stored ordered by keys 

Find/Contains Can find(keyType): – No find(valueType)

Erase Erase takes key or iterator: – Not a value

MultiMap To store list as value, could use map of vector: Can’t use [] with multimap

Multimap Equal_range returns pair of iterators – first : First location where we found a match – second : One past last location of match – first == second : not there