CS253 STL

Purpose

A video introduction is available. For this lab, you will create a program called results.cc and turn it in. First, some STL knowledge.

Overview

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:

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';

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. We will compile it on a CS Dept. computer with g++ -std=c++17 -Wall results.cc, which must not produce any warnings or errors. The program must:

Reads integers, until the user enters zero, into a vector<int>. Don’t put the zero in the vector. No prompting or error-checking is necessary.
Display the integers from the vector<int>, one per line.
Read all the characters from the file /etc/resolv.conf into one big string. By “all the characters”, I mean everything that was in the file—letters, numbers, punctuation, spaces, newlines, etc.: every single byte.
Copy all the characters from the string to a multiset<char>.
Copy all the characters from the multiset<char> to a set<char>.
Display the .size() and characters from the string, set<char>, and multiset<char>, like this:

string: size=length stringcontentswithnoextrapadding
set: size=length setcontentswithnoextrapadding
multiset: size=length multisetcontentswithnoextrapadding

For all three bunches of output, write the container type, as shown, then size=, the number of characters in the container, one space, then everything in the container, with no extra spaces, commas, or any extra separators between the characters, then add a newline. The file contains newlines, so it won’t look pretty.
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 11:59ᴘᴍ MT Saturday, with a 24-hour late period for a 25% penalty.

How to receive negative points:

Turn in someone else’s work.

CS253: Software Development with C++

Spring 2023

STL