Thread: How to use new and delete?

Originally Posted by DecoratorFawn82

When do I use new and delete keywords? And what can I use them to do?

Generally, you would not use them directly, or if you do use new directly, you would hand the result to a smart pointer shortly afterwards. If you do use them directly, it would likely be because you are implementing a container or smart pointer, or have some other special requirements.

I suggest that you work through an introductory book like Accelerated C++ which will first show you how to use things like standard containers and then how to work with pointers along with new and delete.

Originally Posted by DecoratorFawn82

Code:

int Size = 5;
int *ptr = new int(Size);
cout << *ptr << endl;
delete ptr;

this is a perfectly valid use of these keywords. if you allocate an array, you need to remember to delete the whole array with delete[].

Code:

int Size = 5;
int *ptr = new int[Size];
for (int i = 0; i < Size; ++i)
{
  cout << *ptr << endl;
}
delete[] ptr;

like laserlight says though, use a smart pointer or the appropriate container, instead of raw pointers and dynamic arrays. you'll save yourself a lot of headaches and debugging.

Code:

int Size = 5;
int *ptr = new int[Size];
for (int i = 0; i < Size; ++i)
{
  cout << *ptr << endl;
}
delete[] ptr;

With these modifications you just made the code meaningless...

Instead of unlike the 1st one - printing the value of initialized dynamically allocated variable, you now

printing 5 times the 1st member of uninitialized dynamic array.

You would better of with putting ... inside the loop

okay so I missed a change to one line. the point was to demonstrate creating and deleting dynamic arrays, which I did.

don't be so pedantic.

Originally Posted by Elkvis

okay so I missed a change to one line. the point was to demonstrate creating and deleting dynamic arrays, which I did.

Your code demonstrated little of use relevant to using said dynamically allocated arrays. Since the array contents are uninitialised, your loop exhibits undefined behaviour, which is hardly a good thing to demonstrate without explanation.