Are 'new' and 'delete' getting deprecated in C++?

Question

I stumbled upon a quiz that involved array declaration with different sizes. The first thing that came to my mind is that I would need to use dynamic allocation with the new command, like this:

while(T--) {
   int N;
   cin >> N;
   int *array = new int[N];
   // Do something with 'array'
   delete[] array;
}

However, I saw that one of the solutions allowed the following case:

while(T--) {
    int N;
    cin >> N;
    int array[N];
    // Do something with 'array'
}

After a bit of research I read that g++ allows this, but it kept me thinking, in which cases is it then necessary to use dynamic allocation? Or is it that the compiler translates this as dynamic allocation?

The delete function is included. Note, however, that the question in here is not about memory leaks.

Answer 1

Neither snippet you show is idiomatic, modern C++ code.

new and delete (and new[] and delete[]) are not deprecated in C++ and never will be. They are still the way to instantiate dynamically allocated objects. However, as you have to always match a new with a delete (and a new[] with a delete[]), they are best kept within (library) classes that ensure this for you. See Why should C++ programmers minimize use of 'new'?.

Your first snippet uses a "naked" new[] and then never delete[]s the created array. That's a problem. std::vector does everything you need here just fine. It will use some form of new behind the scenes (I won't dive into implementation details), but for all you have to care, it's a dynamic array but better and safer.

Your second snippet uses "variable length arrays" (VLAs), a C feature that some compilers also allow in C++ as an extension. Unlike new, VLAs are essentially allocated on the stack (a very limited resource). But more importantly, they are not a standard C++ feature and should be avoided because they are not portable. They certainly do not replace dynamic (i.e. heap) allocation.