CS253: Software Development with C++

Spring 2023

STL

CS253 STL                

St. Louis Cardinals baseball team logo

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):                 

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';
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

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:                 

  1. 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.
  2. Display the integers from the vector<int>, one per line.
  3. 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.
  4. Copy all the characters from the string to a multiset<char>.
  5. Copy all 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=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.
  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 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.