CS253: Software Development with C++

Spring 2018

STL

See this page as a slide show

CS253 STL

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):

Documentation

http://www.cplusplus.com is great:

Incomplete type

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

vector v;
c.cc: In function 'int main()':
c.cc:1:8: error: missing template arguments before 'v'

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 = {2018, 1492, 1957};
v.push_back(42);
for (size_t i=0; i<v.size(); i++)
    cout << v[i] << '\n';
2018
1492
1957
42

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

[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 = {2018, 1492, 1957};
for (auto val : v)
    cout << val << '\n';
2018
1492
1957

set

set<int> s;
s.insert(3);
s.insert(1);
s.insert(4);
s.insert(1);
s.insert(6);
for (auto val : s)
    cout << val << ' ';
1 3 4 6 

multiset

multiset<char> ms;
ms.insert('b');
ms.insert('a');
ms.insert('n');
ms.insert('a');
ms.insert('n');
ms.insert('a');
for (auto val : ms)
    cout << val;
aaabnn

map

map<int, string> m;
m[253] = "Jack Applin";
m[220] = "Wim Bohm";
m[270] = "Dave Matthews";
for (auto val : m)
    cout << val.second << " is teaching CS" << val.first << endl;
cout << "CS253 is taught by " << m[253] << endl;
cout << "CS222 is taught by " << m[222] << endl;
Wim Bohm is teaching CS220
Jack Applin is teaching CS253
Dave Matthews is teaching CS270
CS253 is taught by Jack Applin
CS222 is taught by 

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 …

Write code that:

  1. Reads integers, until the user enters zero, into a vector<int>.
  2. Write the integers from the vector<int>
  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>.
  7. Explain why they’re different.

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Modified: 2018-02-01T12:06

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