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CS253 STL Containers

Overview

• The most popular containers:
  • vector: variable-length array
  • array: a fixed-length array
  • string: vector<char> and more methods
  • list: doubly-linked list
  • forward_list: singly-linked list
  • set: an ordered binary tree
  • multiset: a set where duplicates are permitted
  • map: a tree of key,value (or a translation)
  • multimap: a map where duplicate keys are permitted
  • deque: a vector with push/pop at either end
  • unordered_set: hash version of set
  • unordered_multiset: hash version of multiset
  • unordered_map: hash version of map
  • unordered_multimap: hash version of multimap

Attributes

Name	Key/Value	Insertion	Append	Search	Ordered
string, vector	value	O(n)	O(1)	O(n)	no
list, forward_list	value	O(1)	O(1)	O(n)	no
[multi]set	value	O(log n)		O(log n)	yes
[multi]map	key/value	O(log n)		O(log n)	yes
deque	value	O(n)	O(1)	O(n)	no
unordered_[multi]set	value	O(1)		O(1)	oddly
unordered_[multi]map	key/value	O(1)		O(1)	oddly

Popular methods

• Universal container methods:
  • default ctor
  • copy ctor
  • operator=
  • ctor(iter, iter)
  • empty()
  • size() / max_size()
  • clear()
  • begin() / end() / cbegin() / cend()
• Popular container methods:
  • ctor(n)
  • rbegin() / rend() / crbegin() / crend()
  • front() / back()
  • insert() / erase()
  • find() / count()

Popular types

• Universal types:
  • value_type
  • iterator
  • const_iterator
  • size_type
• Popular types:
  • key_type
  • reverse_iterator
  • const_reverse_iterator

Thomas Paine

• Thomas Paine was a great writer during the time of the American Revolution.
• He said “These are the times that try men's souls”.

string

string con = "These are the times that try men's souls.";
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41 These are the times that try men's souls.

• This displays a std::string.
• After this, the same code will be shown, but using different containers.
• Sure, we could have just said cout << con; since we’re using a std::string, but but that won’t work for other container types.

vector

string s = "These are the times that try men's souls.";
vector<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41 These are the times that try men's souls.

We can’t initialize a vector directly from a C-style string, so we put it into a C++ string, and initialize the vector from that, using the two-iterator constructor.

array

string s = "These are the times that try men's souls.";
array<char, 41> con;
for (size_t i=0; i<s.size(); i++)
    con[i] = s[i];
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41 These are the times that try men's souls.

A std::array is not a C array. However, it does have a size fixed at compile time. Its storage is all on the stack, with no dynamic memory allocation, so it’s as effecient as a C array. It has typical STL container methods such as .size(), .begin(), .end(), etc. It lacks the two-iterator ctor, perhaps due to its fixed size.

list

string s = "These are the times that try men's souls.";
list<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41 These are the times that try men's souls.

A list is a doubly-linked list. It has a large storage overhead, but insertion is cheap, and you can easily go forward & backward. Unlike a vector, .push_back() never causes reallocation.

forward_list

string s = "These are the times that try men's souls.";
forward_list<char> con(s.begin(), s.end());
for (auto c : con)
    cout << c;

These are the times that try men's souls.

A forward_list (formerly slist) is a singly-linked list. It has a large storage overhead, but insertion is cheap, and you can easily go forward. Curiously, there is no forward_list::size().

deque

string s = "These are the times that try men's souls.";
deque<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41 These are the times that try men's souls.

A deque is a double-ended queue. It’s like a vector, but you can easily push or pop from the front or the back.

set

string s = "These are the times that try men's souls.";
set<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=17  '.Taehilmnorstuy

A set is generally implemented as a binary tree. Hence, it is sorted, has fairly large storage overhead, and has O(log n) find/insertion/deletion times.

multiset

string s = "These are the times that try men's souls.";
multiset<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41        '.Taaeeeeeehhhilmmnorrssssstttttuy

A multiset is like a set, but allows copies.

unordered_set

string s = "These are the times that try men's souls.";
unordered_set<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=17 .luon'ymitar sehT

A unordered_set (formerly hash_set), is a hash table implementation like a set.

unordered_multiset

string s = "These are the times that try men's souls.";
unordered_multiset<char> con(s.begin(), s.end());
cout << "size=" << con.size() << ' ';
for (auto c : con)
    cout << c;

size=41 .luon'ymmitttttaarr       ssssseeeeeehhhT

A unordered_multiset (formerly hash_multiset), is a hash table implementation like a multiset.

map, multimap, unordered_map, unordered_multimap

• map, multimap, unordered_map, and unordered_multimap are like set, multiset, unordered_set, and unordered_multiset, except that they store pairs.
• You can think of them as look-up tables.
• You can think of them as mapping functions.

map example

map<string, double> gpa = {
    { "Jack",  3.998 },
    { "Russ",  4.20  },
    { "Wim",   3.92  },
    { "Craig", 2.0   }
};

for (auto p : gpa)
    cout << p.first << " has a GPA of " << p.second << '\n';
cout << "Jack’s GPA is: " << gpa["Jack"] << '\n';

Craig has a GPA of 2
Jack has a GPA of 3.998
Russ has a GPA of 4.2
Wim has a GPA of 3.92
Jack’s GPA is: 3.998

• A map<A,B> is like a set<pair<A,B>>, ordered by A.
• pair<A,B> has public data members (😲) .first and .second.