Dynamic Memory & Smart Pointers

#include <iostream>
using namespace std;

class Book {
public:
    string title;
    Book(const string &t) : title(t) { cout << "construct " << title << endl; }
    ~Book() { cout << "destroy " << title << endl; }
};

int main() {
    int *n = new int(42);                 // one int, initialised to 42
    cout << *n << endl;
    delete n;

    int *arr = new int[5]{1, 2, 3, 4, 5}; // an array
    for (int i = 0; i < 5; i++) cout << arr[i] << " ";
    cout << endl;
    delete[] arr;                         // arrays need delete[]

    Book *b = new Book("C++ Primer");     // constructor runs
    cout << "reading " << b->title << endl;
    delete b;                             // destructor runs
    return 0;
}

42
1 2 3 4 5 
construct C++ Primer
reading C++ Primer
destroy C++ Primer

#include <iostream>
#include <cstring>
using namespace std;

class Name {
    char *text;
public:
    Name(const char *s) : text(new char[strlen(s) + 1]) { strcpy(text, s); }
    ~Name() { delete[] text; }                                     // 1. destructor
    Name(const Name &o) : text(new char[strlen(o.text) + 1]) {     // 2. copy constructor (deep)
        strcpy(text, o.text);
    }
    Name &operator=(const Name &o) {                               // 3. copy assignment (deep)
        if (this != &o) {                                          // guard against a = a
            char *fresh = new char[strlen(o.text) + 1];
            strcpy(fresh, o.text);
            delete[] text;
            text = fresh;
        }
        return *this;
    }
    void setFirst(char c) { text[0] = c; }
    const char *get() const { return text; }
};

int main() {
    Name a("asha");
    Name b = a;          // copy constructor
    Name c("x");
    c = a;               // copy assignment
    b.setFirst('U');
    c.setFirst('N');
    cout << a.get() << " " << b.get() << " " << c.get() << endl;   // each has its own buffer
    return 0;
}

asha Usha Nsha

#include <iostream>
#include <memory>
using namespace std;

struct Sensor {
    int id;
    Sensor(int i) : id(i) { cout << "sensor " << id << " on" << endl; }
    ~Sensor() { cout << "sensor " << id << " off" << endl; }
};

int main() {
    unique_ptr<Sensor> a = make_unique<Sensor>(1);
    cout << "reading sensor " << a->id << endl;
    // unique_ptr<Sensor> b = a;          // error: cannot copy a unique_ptr
    unique_ptr<Sensor> b = std::move(a);  // ownership moves to b
    cout << "a is " << (a ? "set" : "empty") << ", b owns sensor " << b->id << endl;
    {
        auto c = make_unique<Sensor>(2);
    }                                     // c's sensor freed here automatically
    cout << "end of main" << endl;
    return 0;
}                                         // b's sensor freed here

sensor 1 on
reading sensor 1
a is empty, b owns sensor 1
sensor 2 on
sensor 2 off
end of main
sensor 1 off

#include <iostream>
#include <memory>
#include <string>
using namespace std;

struct Playlist {
    string name;
    Playlist(string n) : name(n) {}
    ~Playlist() { cout << "deleting playlist " << name << endl; }
};

int main() {
    shared_ptr<Playlist> mine = make_shared<Playlist>("Coding Lo-fi");
    cout << "owners: " << mine.use_count() << endl;
    {
        shared_ptr<Playlist> friendCopy = mine;
        cout << "owners: " << mine.use_count() << endl;
    }
    cout << "owners: " << mine.use_count() << endl;
    mine.reset();                          // last owner gone: object deleted
    cout << "done" << endl;
    return 0;
}

owners: 1
owners: 2
owners: 1
deleting playlist Coding Lo-fi
done