Study Note

C++ Learning Journey Day11

Symbols count in article: 1.3k Reading time: 8 mins.

Section 22: I/O Streams

Streams

  1. Stream is a flow of data or flow of characters. Streams are used for accessing the data from outside program.
  2. Here are the types of stream.
    • istream: cin >>
    • ostream: cout <<
    • ifstream
    • ofstream

Writing in a File

  1. Example. 
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    #include <iostream>
    #include <fstream>

    using namespace std;

    int main()
    {
        ofstream ofs("My.txt", ios::trunc);
        ofs << "John" << endl;
        ofs << 25 << endl;
        ofs << "cs" << endl;
        ofs.close();

        return 0;
    }

Reading From a File

  1. Example. 
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    #include <iostream>
    #include <fstream>

    using namespace std;

    int main()
    {
        ofstream ofs("My.txt", ios::trunc);
        ofs << "John" << endl;
        ofs << 25;
        ofs.close();

        ifstream ifs;
        ifs.open("My.txt");
        if (!ifs.is_open())
            cout << "File can't be open" << endl;
        string str;
        int x;
        ifs >> str;
        ifs >> x;
        cout << str << " " << x << endl;

        if (ifs.eof())
            cout << "end of file reached";
        ifs.close();


        return 0;
    }
    ====OUTPUT====
    John 25
    end of file reached

Serialization

  1. Example. 
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    #include <iostream>
    #include <fstream>

    using namespace std;

    class Student
    {
    public:
        string name;
        int roll;
        string branch;
        friend ofstream & operator<<(ofstream &ofs, Student &s);
        friend ifstream & operator>>(ifstream &ifs, Student &s);
    };

    ofstream & operator<<(ofstream &ofs, Student &s)
    {
        ofs << s.name << endl;
        ofs << s.roll << endl;
        ofs << s.branch << endl;

        return ofs;
    }

    ifstream & operator>>(ifstream &ifs, Student &s)
    {
        ifs >> s.name >> s.roll >> s.branch;
        return ifs;
    }

    int main()
    {
        Student s1;
        s1.name = "Khan";
        s1.roll = 10;
        s1.branch = "CS";

        ofstream ofs("Student.txt", ios::trunc);
        ofs << s1;
        ofs.close();

        Student s2;
        ifstream ifs("Student.txt");
        ifs >> s2;
        cout << "Name " << s2.name << endl;
        cout << "Roll " << s2.roll << endl;
        cout << "Branch " << s2.branch << endl;

        return 0;
    }
    ====OUTPUT====
    Name Khan
    Roll 10
    Branch CS

Text and Binary Files

  1. Text files are human readable and binary files are a machine readable.
  2. Binary file is faster and take less space.

Manipulators

  1. Manipulators are used for enhancing streams or formatting streams.
  2. Manipulators for integer: hex, oct, dec, fixed, scientific. Example. 
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    cout << endl;
    cout << "\n";

    cout << hex << 163 << endl;

    cout << fixed << 125.731 << endl;
    cout << scientific << 125.731 << endl;
    ====OUTPUT====


    a3
    125.731000
    1.257310e+02
  3. Other Manipulators: set(), left, right, ws.

Section 23: STL

Why STL

  1. STL = Standard Template Library.
  2. Storing the collection of values, you need data structure.
  3. You want to save data in efficient time and space, you need STL.

Types of Data Structures

  1. Data Structures.
    • Array
    • Singly LinkedList
    • Doubly LinkedList
    • Stack
    • Queue
    • Deque
    • Priority Queue
    • map
    • set

STL Classes

  1. STL has the following classes.
    • Algorithms: search(), sort(), binary-search(), reverse(), concat(), copy(), union(), intersection(), merge(), Heap().
    • Containers(Contain collection of data)
      • vector(self-managed array, it can resize the length of array automatically): push_back(), pop_back(), insert(), remove(), size(), empty().
      • list(doubly linkedList): push_front(), pop_front(), push_back(), pop_back(), insert(), remove(), size(), empty(), front(), back().
      • forward_list(singly linkedList): push_front(), pop_front(), push_back(), pop_back(), insert(), remove(), size(), empty(), front(), back().
      • deque: push_front(), pop_front(), push_back(), pop_back(), insert(), remove(), size(), empty(), front(), back().
      • priority_queue(max heap): push(), pop(), empty(), size().
      • stack(LIFO)
      • set(unique element)
      • multiset(allow duplicate)
      • map(Hashtable): It can store <key, value> pair. It has to contain unique keys.
      • muttimap: keys can be duplicated, but same key value map can’t be here.
    • Iterators
  2. You can focus on add and remove data, here is an example. 
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    #include <iostream>
    #include<vector>

    using namespace std;

    int main()
    {
        vector<int> v = { 10, 20, 40, 90 }; // default size is 16
        v.push_back(25);
        v.push_back(70);
        v.pop_back();

        for (int x : v)
            cout << x << " ";

        cout << endl;

        vector<int>::iterator itr;
        for (itr = v.begin(); itr != v.end(); itr++)
            cout << *itr << " ";
        
        return 0;
    }
  3. If you change the iterator’s data, you will change the data directly. 
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    #include <iostream>
    #include<vector>

    using namespace std;

    int main()
    {
        vector<int> v = { 2, 4, 6, 8, 10 }; // default size is 16
        v.push_back(20);
        v.push_back(30);

        cout << "using Iterator" << endl;
        vector<int>::iterator itr;
        for (itr = v.begin(); itr != v.end(); itr++)
            cout << ++*itr << " ";

        cout << endl;

        for (int x : v)
            cout << x << " ";

        return 0;
    }
    ====OUTPUT====
    using Iterator
    3 5 7 9 11 21 31 
    3 5 7 9 11 21 31
  4. You can change vector to list or forward_list. 
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    #include <iostream>
    #include<forward_list>

    using namespace std;

    int main()
    {
        forward_list<int> v = { 2, 4, 6, 8, 10 }; // default size is 16
        v.push_front(20);
        v.push_front(30);

        cout << "using Iterator" << endl;
        forward_list<int>::iterator itr;
        for (itr = v.begin(); itr != v.end(); itr++)
            cout << ++*itr << " ";

        cout << endl;

        for (int x : v)
            cout << x << " ";

        return 0;
    }
  5. You can not change set value and it use insert to add data. 
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    #include <iostream>
    #include<set>

    using namespace std;

    int main()
    {
        set<int> v = { 2, 4, 6, 8, 10 }; // default size is 16
        v.insert(20);
        v.insert(30);

        cout << "using Iterator" << endl;
        set<int>::iterator itr;
        for (itr = v.begin(); itr != v.end(); itr++)
            cout << *itr << " ";

        cout << endl;

        for (int x : v)
            cout << x << " ";

        return 0;
    }

Map Classes

  1. Example. 
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    #include <iostream>
    #include<map>

    using namespace std;

    int main()
    {
        map<int, string> m;
        m.insert(pair<int, string>(1, "john"));
        m.insert(pair<int, string>(2, "Ravi"));
        m.insert(pair<int, string>(3, "Khan"));

        map<int, string>::iterator itr;
        for (itr = m.begin(); itr != m.end(); itr++) {
            cout << itr->first << " " << itr->second << endl;
        }

        map<int, string>::iterator itr1;
        itr1 = m.find(2);
        cout << "Value found is ";
        cout << itr1->first << " " << itr1->second << endl;


        return 0;
    }
    ====OUTPUT====
    1 john
    2 Ravi
    3 Khan
    Value found is 2 Ravi

Disclaimer

I took this course from Udemy, which is Learn C++ Programming -Beginner to Advance- Deep Dive in C++. I only took some notes of this amazing course for my personal future uses and share my thoughts with my peers. If you like it, you should take the course from Udemy too.

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