CS253 STL                

The STL is the Standard Template Library. It wasn’t originally part of C++; it was a library written at HP. It’s now an official part of C++, but the name remains.                 

We will discuss these containers (there are more):                 

• vector: A linear collection, like an array.
• string: Pretty much a vector<char>, with specialized methods
• list: A doubly-linked list
• set / multiset: A sorted collection (a tree)
• map / multimap: A sorted collection of pairs, a mapping

Documentation                

https://cplusplus.com is great:

• https://cplusplus.com/vector
• https://cplusplus.com/string
• https://cplusplus.com/list
• https://cplusplus.com/set
• https://cplusplus.com/map

Incomplete type                

There is no type called simply vector. You can’t do this:                 

vector v;

c.cc:1: error: class template argument deduction failed:

It’s a vector of … what? You have to decide. Give it a type:                 

vector<int> a;
vector<string> b;
vector<const char *> c;
cout << "Hooray!\n";

Hooray!

.size()                

All STL containers have a current size, initially zero.                 

#include <vector>
#include <string>
#include <set>
#include <iostream>
using namespace std;
int main() {
    vector<int> vi;
    string str;
    set<double> sd;
    cout << "vector size: " << vi.size() << '\n'
         << "string size: " << str.size() << '\n'
         << "set size: " << sd.size() << "\n\n";
    vi.push_back(10);
    str.push_back('J'); str += "ck"; str.insert(1, "a");
    sd.insert(7.6); sd.insert(1.2); sd.insert(7.6);
    cout << "vector size: " << vi.size() << '\n'
         << "string size: " << str.size() << '\n'
         << "set size: " << sd.size() << '\n';
}

vector size: 0
string size: 0
set size: 0

vector size: 1
string size: 4
set size: 2

Iterating over a vector:                

vector<int> v = {2024, 1492, 1957};
v.push_back(42);
for (size_t i=0; i<v.size(); i++)
    cout << v[i] << '\n';

2024
1492
1957
42

Why size_t? Why not just int? Because vector::size() returns an unsigned type, and the compiler will complain if we compare signed and unsigned integers. size_t is an appropriate unsigned type.                 

vector<int> v;
for (int i=0; i<v.size(); i++)
    cout << v[i] << '\n';

c.cc:2: warning: comparison of integer expressions of different signedness: 
   'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'}

[subscript ] only works for vector and string. Indexing would be expensive for set and list. For map, the subscript represents the key, and returns the value.                 

Easier iteration                

If you don’t need the index:                 

vector<int> v = {2024, 1492, 1957};
for (auto val : v)
    cout << val << '\n';

2024
1492
1957

set                

set<char> s;
for (char c : "bingeing"s)
    s.insert(c);
for (auto val : s)
    cout << val;

begin

• You recall that "bingeing"s is a C++ string object, not an old null-terminated C string.
• How did “bingeing” become “begin”⁇

multiset                

multiset<char> ms = {'l', 'o', 'y', 'a', 'l'};
for (auto val : ms)
    cout << val;

alloy

map                

map<char, string> grades = {
    {'W', "Withdraw"},
    {'A', "Excellent"},
    {'B', "Better than average"},
    {'C', "OK"},
    {'D', "Not passing"},
    {'F', "Failure"},
};
grades['I'] = "Incomplete";
for (auto p : grades)
    cout << p.first << " means " << p.second << '\n';
cout << "If you get it all right, you are: " << grades['A'] << '\n';
cout << "In CS253 last year, I got a Q: " << grades['Q'] << '\n';

A means Excellent
B means Better than average
C means OK
D means Not passing
F means Failure
I means Incomplete
W means Withdraw
If you get it all right, you are: Excellent
In CS253 last year, I got a Q: 

Why did the for-loop produce the lines in that order?                 

Linked List                

list<int> l;
for (int i=0; i<10; i++)
    l.push_back(rand() % 100);
for (auto val : l)
    cout << val << ' ';

83 86 77 15 93 35 86 92 49 21 

Now …                

Create a program results.cc that:

1. Reads integers, until the user enters zero, into a vector<int>. Don’t put the zero in the vector. No prompting is necessary.
2. Write the integers from the vector<int>, one per line.
3. Read all the characters from the file /etc/resolv.conf into one big string.
4. Copy the characters from the string to a multiset<char>.
5. Copy the characters from the multiset<char> to a set<char>.
6. Display the .size() and characters from the string, set<char>, and multiset<char>, like this:
   string: size=37 string contents with no extra padding
   set: size=length contents
   multiset: size=length contents
   The file contains newlines, so it won’t look that nice.
7. Add a comment block to your program, starting with “// QUESTION 7”, that explains why the sizes from the previous question aren’t all the same. I want an explanation—merely stating “this one is 10, but this one is 20” is not good enough.

How to submit your work:                

In Canvas, check in the file results.cc to the assignment “Lab03”. It’s due 10:00:00ᴘᴍ MT Saturday, with a 24-hour late period for a 25% penalty.                 

How to receive negative points:                

Turn in someone else’s work.