The University of Iowa
The College of Liberal Arts and Sciences
Department of Computer Science

Programming Languages and Tools:

CS:3210:0001

Lecture/Lab #26

Programming with C++

Unordered associative containers, function templates

Warm up

  • What's the main difference between std::map and std::multimap?
  • Given the following definitions, how would you implement the print_all function that prints all people who live in a certain zip code?
struct person
{
    std::string first_name;
    std::string last_name;
    std::string phone_number;
};

using people_by_zipcode = std::multimap<std::string,person>;

void print_all( 
    people_by_zipcode const& address_book, 
    std::string const& zip_code 
    );

Unordered Associative Containers

  • Require a hash function and do not maintain an order among its elements

  • unordered_map<Key,T>

  • unordered_multimap<Key,T>

  • unordered_set<T>

  • unordered_multiset<T>

  • O(1) average lookup/insertion/deletion time
  • O(n) worst-case lookup/insertion/deletion time

https://repl.it/@agurtovoy/lab26-unordered-multimap

  • Default hash function implementation (std::hash<T>) for std::string and all the basic integral type keys comes with the standard library

Function templates

How do we write a function (or a family of functions) sum such that all of the following compiles and does what we want:

Problem:

sum( vector<int>({ 10, -1, 42 }) )
sum( vector<double>({ 10.5, -1.1, 42.7 }) )
sum( vector< complex<double> >({ 
        complex( 10.5, 1.0 ), 
        complex( -1.1, 0.0 ), 
        complex( 42.7, -1.0 ) 
        }) )

https://repl.it/@agurtovoy/lab26-function-templates

Exercise 1

Implement a generic find_value function that passes the tests​

https://repl.it/@agurtovoy/lab26-exercise1

  • Open the exercise template

  • Write your code, press Run to test

  • When you're done, grab your Repl's link and send it as a direct message to me (agurtovoy)

  • Click on the corresponding option in the "Lab26 exercises" poll in #general

Programming with C++, Fall 2019, Lecture #26

By Aleksey Gurtovoy

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Programming with C++, Fall 2019, Lecture #26

Unordered associative containers, function templates

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