gBard Ans: Different types of smart pointers in C++

 There are several different types of smart pointers in C++. Here are some of the most common ones:

• Unique pointers: Unique pointers are a type of smart pointer that owns the object that it points to. This means that there can only be one unique pointer to an object at a time. When a unique pointer goes out of scope, the object that it points to is automatically deleted.
• Shared pointers: Shared pointers are a type of smart pointer that share ownership of the object that they point to. This means that there can be multiple shared pointers to an object at a time. When the last shared pointer to an object goes out of scope, the object is automatically deleted.
• Weak pointers: Weak pointers are a type of smart pointer that do not own the object that they point to. This means that the object that the weak pointer points to can be deleted even if the weak pointer is still in scope. Weak pointers are often used to prevent circular references between objects.
• Auto pointers: Auto pointers are a type of smart pointer that are automatically created and deleted by the compiler. Auto pointers are a convenient way to use smart pointers, but they can be less flexible than other types of smart pointers.

Here is a table that summarizes the different types of smart pointers in C++:

Smart pointer type	Ownership	When the object is deleted
Unique pointer	Owns the object	When the unique pointer goes out of scope
Shared pointer	Shares ownership of the object	When the last shared pointer to the object goes out of scope
Weak pointer	Does not own the object	When the object that the weak pointer points to is deleted
Auto pointer	Automatically created and deleted by the compiler	When the object that the auto pointer points to is deleted

I hope this helps!

gBard Ans: Example of using different kind of smart pointers in C++

 Example of using the different types of smart pointers in C++:

C++

#include <iostream>
#include <memory>

using namespace std;

class MyObject {
public:
  MyObject() {
    cout << "MyObject created" << endl;
  }

  ~MyObject() {
    cout << "MyObject deleted" << endl;
  }
};

int main() {
  // Create a unique pointer to a MyObject.
  unique_ptr<MyObject> my_object(new MyObject());

  // The MyObject object will be deleted when the unique pointer goes out of scope.

  // Create a shared pointer to a MyObject.
  shared_ptr<MyObject> my_shared_object(new MyObject());

  // There can be multiple shared pointers to the same MyObject object.
  shared_ptr<MyObject> my_other_shared_object(my_shared_object);

  // The MyObject object will be deleted when the last shared pointer to it goes out of scope.

  // Create a weak pointer to a MyObject.
  weak_ptr<MyObject> my_weak_object(my_shared_object);

  // The weak pointer does not own the MyObject object, so it can be deleted even if the weak pointer is still in scope.

  return 0;
}

This code will print the following output to the console:

Code snippet

MyObject created
MyObject deleted

The first line of output is printed when the MyObject object is created. The second line of output is printed when the MyObject object is deleted. The MyObject object is deleted when the unique pointer goes out of scope.

Notes Untutu GNU C/C++ compiler: How to configure gcc/g++ version in ubuntu?

 First erase the current update-alternatives setup for gcc and g++:

sudo update-alternatives --remove-all gcc 

sudo update-alternatives --remove-all g++

--

Use sudo apt-get install gcc-<version1> gcc-<version2> g++-<version1> g++-<version2>; to install versions

eg sudo apt-get install gcc-11 gcc-13 g++-11 g++-13;

--

Then run commands:

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-<version1> 10

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-<version2> 20

sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-<version1> 10

sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-<version2> 20

sudo update-alternatives --install /usr/bin/cc cc /usr/bin/gcc 30

sudo update-alternatives --set cc /usr/bin/gcc

sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++ 30

sudo update-alternatives --set c++ /usr/bin/g++

--

Finally to configure default version usage use following commands

sudo update-alternatives --config gcc

sudo update-alternatives --config g++

--

Check version using command

gcc --version;

g++ --version;

Notes: C++ Codeblocks Postgres Connection Ubuntu Settings

 Install in system below

sudo apt install libpqxx-dev

------------

In codeblocks right click project->build options

search directories tab->Compiler tab

give path for pqxx. Normally this is /usr/include/pqxx

Right click project->build options

Linker Settings tab

add following Link libraries :- pqxx, pq

---------

Thats all