Why are dynamic 2d arrays deleted the same way as dynamic 1d array?

[stonedviper]

Hello!

My question is why are dynamic 2d arrays deleted the same way as a dynamic 1d array?

I mean this is how they're declared

    const int rowcol=3;
    int **matrix;
    matrix=new int *[rowcol];
    for(int i=0;i<rowcol;i++)*(matrix+i)=new int [rowcol];

but we delete them as a 1d array why? i mean we do extra initialization but yet we delete the same way as 1d array.
also i tried this

   delete [rowcol] matrix[];

but it crashes or gives me a compilation error and sometimes it will work without a problem depending on the compiler.

thank you for your answers

[Chervil]

Each new should have a corresponding delete.
Each new[] should have a corresponding delete[].

In your example above, the matching deletes would look something like this:

    for (int i=0; i<rowcol; i++)
        delete []  *(matrix+i);
        
    delete [] matrix;  

[stonedviper]

I see thank you!
By the way I know that this isn't related to my question but I want to know out of curiosity.
Why do some people delete their dynamic variables with nullptr,or set them to nullptr after deleting them? and what's the difference between the three?

[AbstractionAnon]

Why do some people delete their dynamic variables with nullptr

Are you asking this:

  Foo * foo = new Foo;
//  Mess with foo
  foo = nullptr;  // This does NOT delete foo.  This is a memory leak 

or set them to nullptr after deleting them?

After a delete foo; foo still points somewhere in memory, although now it's a logical error to dereference foo. By setting foo to nullptr, you're guaranteed a program trap due to an illegal address if you attempt to dereference foo (at least on architectures where memory address 0 is not a legal address).

IMO, this is a good practice in the specific case where the pointer has a lifetime longer than what was deleted. If the pointer immediately goes out of scope after being deleted, there is really no need to set it to nullptr.

[stonedviper]

Thank you again.
Though you did open lot of questions for me.I don't think it will be a great idea to ask them since my main question has been answered.But I will ask this can you or someone explain what it means to be legal?Or direct me to a guide or something to read it.

Thank you!