The shared_ptr smart pointer is used when a group of shared_ptr objects shares the ownership of a heap-allocated object. The shared_ptr pointer releases the shared object when all the shared_ptr instances are done with the use of the shared object. The shared_ptr pointer uses the reference counting mechanism to check the total references to the shared object; whenever the reference count becomes zero, the last shared_ptr instance deletes the shared object. 

Let's check out the use of shared_ptr through an example, as follows:

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

class MyClass {
  private:
    static int count;
    string name;
  public:
    MyClass() {
      ostringstream stringStream(ostringstream::ate);
      stringStream << "Object";
      stringStream << ++count;

      name = stringStream.str();

      cout << "\nMyClass Default constructor - " << name << endl;
    }

    ~MyClass() {
      cout << "\nMyClass destructor - " << name << endl;
    }

    MyClass ( const MyClass &objectBeingCopied ) {
      cout << "\nMyClass copy constructor" << endl;
    }

    MyClass& operator = ( const MyClass &objectBeingAssigned ) {
      cout << "\nMyClass assignment operator" << endl;
    }

    void sayHello() {
      cout << "Hello from MyClass " << name << endl;
    }

};

int MyClass::count = 0;

int main ( ) {

  shared_ptr<MyClass> ptr1( new MyClass() );
  ptr1->sayHello();
  cout << "\nUse count is " << ptr1.use_count() << endl;

  {
      shared_ptr<MyClass> ptr2( ptr1 );
      ptr2->sayHello();
      cout << "\nUse count is " << ptr2.use_count() << endl;
  }

  shared_ptr<MyClass> ptr3 = ptr1;
  ptr3->sayHello();
  cout << "\nUse count is " << ptr3.use_count() << endl;

  return 0;
}

The output of the preceding program is as follows:

MyClass Default constructor - Object1
Hello from MyClass Object1
Use count is 1

Hello from MyClass Object1
Use count is 2

Number of smart pointers referring to MyClass object after ptr2 is destroyed is 1

Hello from MyClass Object1
Use count is 2

MyClass destructor - Object1