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